How do i get better looking nails?

ive bitten my nails for as long as i can remember. i keep them so low that they dont pass my finger tips. sometimes it hurts and its hard to pick little things up!!! haha. they look ugly too. the last time that i tried to grow my nails out, they were very thin, brittle, and yellow!!!! what can i do to make sure my nails dont grow out yellow? also, im using a nail hardener to thicken my nails and stop the breaking. what else could i do?