So after the immense success of my Ganondorf guide (with immense in the largest quotation marks this website will afford), I realized that it was my destiny to tell people how to play video games. But I realized, after a brief trip through the comments section, that much of the divinely inspired wisdom from the guide may have been lost due to people not being all that familiar with Smash terminology/how to play the game competitively. So with that said, here's a guide on how to play competitive Smash 4 semi well.
Before we jump into that, though, here's a brief list of terminology I'll be using throughout.
Start Up: The amount of time it takes for the move you're performing to actually come out. Basically this the wind up of sorts, the amount of time the move takes before it will actually hit anyone
Recovery: The amount of time it takes after a move has finished before you regain control of your character
Rushdown: This is a playstyle which implies trying to consistently put pressure on your opponent. When you rush someone down, you're getting up close and personal, using melee/short ranged attacks to keep them on the defensive
Zoning: Zoning is the opposite of rushdown, trying to keep some distance from your opponent and poke them with ranged attacks
Hit Confirm: This refers to throwing out a safe move, and, if the move connects, following it up with another move afterwards. If the first attack misses, then you don't go for the second.
Additionally, here's a standard control scheme for those just getting into the game. All of these controls are assigned to the 3DS, though they should translate directly to the Gamecube/Gamepad/Pro Controller, with the exception of
L: Translates to Z on Gamecube and LT/RT on Gamepad/Pro
R: Translates to L/R on Gamecube and LB/RB on Gamepad/Pro
Double Tap L Stick: Translates to simply holding the stick all the way to the side
The first thing I'd suggest when trying to begin playing Smash competitively is pick a character that you want to use. Lots of people say that you should get used to the way a game works before trying to main a character, but for me, I find that it's much easier to get a grasp on the way one character works and extrapolate that to other characters as opposed to trying to get a general idea of how every single character on the roster works and then pick someone from that. Particularly so with a roster as large as Smash's; attempting to figure out the basics of every single character is an utter headache. With that said, this may just be me, and if you can manage it, feel free to try the other method out. Certainly will save you a lot of hassle if you find out you really don't like the character you picked.
With that said, some of the easier characters to just pick up and play are: Link, Mario, Little Mac, Bowser, and Pit. All of these characters have pretty good KO options, and, perhaps more importantly, aren't all that susceptible to zoning tactics (also known as "spamming" to some). None of these characters require especially good timing to do well with, either, so there's a bit more margin for error than for someone like Captain Falcon or Sheik.
So, if you've found a character you enjoy playing with, it's time to get into the basics. Probably the first thing worth doing when you choose a character is to identify both their strengths and weaknesses. First off, look for where your character wants to be in any given fight. Do they want to consistently be hounding the opponent, trying to put as much pressure on them as possible? Do they want to be on the other side of the stage, trying to keep their opponent far away? Or do they want to be somewhere inbetween?
Link, for instance, probably prefers to be somewhere in the middle, since most of his melee attacks are fairly punishable if they are blocked/if they miss. Yet, at the same time, he doesn't function all that well as a straight up zoning character, since many of his projectiles have a good amount of start up time and can be punished if the opponent knows they're coming (plus, a number of characters have much better zoning options than Link). Link arguably thrives off being unpredictable as to whether he'll attack you with projectiles or go for a more rushdown heavy approach, so Link wants to remain somewhere inbetween. Other characters will have different areas where they function best, however. Characters like Megaman and Duck Hunt Dog are best at a distance, while Ike/Donkey Kong can really only function when rushing their opponent down.
Once you've gotten that established for your characters of choice, your next step is to figure out how exactly you plan to accomplish that. Shulk, for instance, likes to be up close and personal with his opponents. Achieving this may seem tricky at first, however, because many of his moves are extremely punishable. So the next step then is to figure out safe attacks and spacing. Safe attacks are moves you can use that, if you perform it correctly, cannot be punished by your opponent. Shulk's Neutral Air, for instance, is surprisingly safe; if spaced correctly, very few opponents can punish it due to its short recovery. This makes Shulk's Neutral Air one of his best tools for trying to pressure opponents; because it's so difficult to punish, it's a low risk option that you can consistently use. If your attack is blocked, no big deal. If it hits, you've done damage. Finding low risk attacks is key to doing well, especially if you plan on using that attack frequently.
Spacing, meanwhile, is the other side of this coin, and is arguably equally important. Borrowing the example of Shulk's Neutral Air, this attack is safe if spaced correctly. If you're too close to your opponent when you preform this attack, it is actually quite punishable. If you're a short distance away, however, the attack is much harder to punish. The reason for this is simple; after the attack ends, your opponent has a brief window of opportunity (recovery frames) in which to hit you. If you're nearby your opponent when the attack ends, then your opponent can use short range attacks, which often come out extremely quickly, to hit you within those recovery frames. If you're a bit further away, however, your opponent has to use a ranged attack (usually with longer start up time), or move to you and then use a quick attack. In either case, by the time your opponent does either, the window of opportunity to hit you will have passed and you'll be free to block the attack. The key here is to figure out a safe attack, and figure out at what range the attack is safe. Shulk's Neutral Air will hit an opponent at a short distance or right next to them, but it is only safe at a short distance.
So now you have a character, have a general idea of where you want to be with that character, and have at least one or two attacks that you can use with that character to consistently attack your opponent with. But what about the other moves? Surely they're not just there for show. Well, no, they aren't (with the exception of possibly Jigglypuff's Up B), and part of learning the character is to figure out when to throw them in and what they're useful for. Consider Zero Suit Samus for a second. When ZSS is close to an opponent, she only has a couple of safe options; her neutral air is one if spaced well, jab combo is decent, U-Tilt is ok, and that's about it. When she's a short distance away, however, her moveset opens up dramatically. Side B becomes an excellent poking option, Neutral B is an effective zoning tool/useful for creating a window to attack your opponent in, and Down Smash becomes an extremely useful tool for punishing anyone trying to rush their way in. Essentially, many of your moves which don't seem particularly safe/useful at first may actually be quite useful; you'll just have to find the distance at which they are useful.
Keep in mind that your opponent's attacks can and should influence how you play as well. Some attacks that may be safe from a certain distance against Donkey Kong may very well (and generally aren't) going to be safe against Sonic. Additionally, your entire playstyle may have to change depending on who you're fighting. If you're playing Robin, for instance, you may want to keep someone like Shulk away if at all possible, while you may want to try and rush someone like Duck Hunt Dog down.
So now that we've taken care of that, you're in a good position to rack up damage on your opponent. The next step becomes actually KO-ing them. Since Smash isn't like other fighting games, killing an opponent and dealing damage aren't as connected as they would be otherwise. For this, you need to figure out what your KO-ing moves are. For some characters, like Ganondorf and Bowser, this isn't as big of an issue, as basically all of their moves are KO moves. Others, however, only have a couple of moves that can reliably KO opponents, so figuring out what those are and not using them until your opponent is at higher percentages is important.
For instance, while Ness has a lot of options for racking up damage, he only has a few moves that will kill people. His smash attacks will, as will most people's Smash attacks, but landing one of those is quite tricky. Instead, one of Ness's best KO options (and generally much easier to get) is his Back Throw, which can KO at surprisingly low %s, especially if he's grabbing you near a ledge.
With that said, if you play Ness, you're going to want to avoid simply back throwing every time you grab an opponent. Why? Well, it's due to something called stale move negation, which basically means that on any given stock, the more you use an attack, the less powerful it will become. This is another reason why it's so important to separate KO moves from damage moves; you want to use your damage moves to rack up %s, and then use your KO moves to actually kill your opponent once they're high enough. If you use your KO moves to deal damage, it won't be powerful enough to kill when you're in range to actually kill them.
Running with this example a bit further, Ness's Side B is an excellent tool that can trap opponents and can allow for him to run up and grab them. Once he hits them with Side B, while the opponent is at lower %s, he may want to follow it up with another Side B, a sprint attack, or run up and forward throw them. When they're at higher %s, however, he'll want to use his back throw to actually try to kill them. He doesn't waste his back throw power earlier, so it's still perfectly strong and ready to kill when the time comes.
I won't go too much further, as going beyond this requires getting into more complicated stuff, but I'll end with a few final tips.
1) Using the same move over and over again (without any way to cover it) is almost assuredly a bad idea. For instance, if @Indigogeek is being a fool and consistently using his sprint attack, he's going to get grabbed and thrown every single time. Mix up your attack patterns
2) Find ways to make useful attacks that are generally unsafe, safe. For instance, ZSS's grab is extremely useful due to its range and its throw combo potential, but it's incredibly unsafe if it misses. However, ZSS's Neutral B, if it connects, can often times be hit-confirmed into a throw/air combo. As a side note, people have gotten extremely angry at me for doing this a lot
3) Shield Rolling may seem like an appealing method of movement at first, but it's far less safe than it seems. Shield Roll is extremely vulnerable during start up and ending animations, and can be punished quite easily if your opponent predicts it
4) It's oftentimes worth having a second character that you know how to play at least decently well, because many characters have at least a few awful matchups. Basically, this means that, if both characters are played by an equally skilled person, one character will beat the other almost every time. A few examples of said terrible matchups are: Rosalina-Ganondorf, Lucario-Meta Knight, Pikachu-Wii Fit Trainer, and Basically Everyone-Donkey Kong. Having a backup character can give you a chance in some of these terrible matchups
5) On that note, don't play Donkey Kong unless you really want to lose. He's just bad. Fun to play with, but undeniably awful
Hopefully this helps a bit. This by no means covers everything, and there's tons of stuff I didn't go over. Apologies, I'm lazy