I agree with Luke..
but... I think you should upload shit in order to get feedback, criticism and advice. Theres nothing wrong with refining your ish before uploading but you gotta start somewhere. The one of the best things about NGs, sometime people will give you some useful words, instead of just nonsense hate.
As for the lyrics; I say, its like flow, practice makes perfect. This is gonna sound cheesy but reading is one best things for improving your writing ability. I used to write rhymes before I was reading for my leisure , and I was doing real simple single syllable shit... but when I started reading more and more, my vocab and knowledge increased greatly. Also became more aware of other literary devices I could use in my writing. Lol, it still sounds corny, but I found that it worked for me.
As for flow; freestyle. Work on your natural flow, build that confidence in the force and just go with it. Record em, listen to em, then move on. I try to do at least one freestyle a week. Im still pretty bad at freestyling but it is what it is.
Keep it droppin Urbs