I've been MOCing for about a year, but since I've literally been working on a single MOC this whole time, I'm about as new as you are. However, I'll share what I can:
•Use the Vitruvian Man as a guide. I recently started using this and it is super helpful on MOC proportions.
•Always see what others are building. Even look at Moc building tutorials. You don't need to copy what you see, but use it as inspiration.
•Never be shy to ask for help. (Oh you already know this step. Good job!)
•The color wheel is your friend.
•When you pick a theme, don't base your moc off one example. Look at MANY examples and see what sticks.
•Always experiment. Even if it doesn't look like a piece for a leg, it could be.