Here, I can't even build titans that will look good and not sloppy and I never bought any pieces off bricklink or ebay and I don't have good lighting either. I'm a lot like you in a sense. U all have the potential to becoming a decent moccer in my eyes and the only thing separating u and the best is experience.
What I did is that I observed others mocs and see what is good about it. They might even give u inspiration! but never copy, that's a big NO. See what pieces are used and not used very often lift the technic lift arms. Dont build titans or mocs like sidorak and u can tell by how many good mocs are using that technique. the answer is none.
The other tip is to mess with pieces for HOURS. think outside the box. Try to show ur personality in the moc, create new building techniques, use appealing colour choices. Lastly, talk to some experience moccers and ask what is good and bad, but make sure the mocs are in the proto stage so u can improve and use their advice.
lastly, try to get a good/decent background and light. This I think is the MOST important. the lighting needs to be able to show the viewer the moc and make it pleasant to look at. with the background, all I used is new christmas wrapping paper (the white side) this i best for a lot of mocs but it doesn't work with white so use poster boards.
I hope this helps and good luck!