For me it could be a certain amount of things.
Such as feet, and shoes to fit over them and still look natural. Or feet at certain angles, like from behind.
Or drawing people at extreme angles/perspectives. Or 1/3 picture and have one side or the other look "off".

And backgrounds. I suck at drawing them, I really have a tough time with these things. But still I try to draw them, and try to improve myself, only way to get better

Well if you have a problem with eyes, is keep drawing them.
Practice, practice, PRACTICE!!!
Read up on some online tutorials, see if there are books that could look helpful in your local library Ask for help from you teacher...or friends you know who also draw.
That's all I could say that might be of any use, rally hope this helps in some way. :)