Practice helps of course, but it's how you practice that matters. For aiming there are two things I do that I know work; Custom game, you VS a team of 6 HARD A.I. Ana heroes. Put headshots only on and switch the game mode to SKIRMISH. Your footwork (w,s,a,d) should also improve with time in this mode.
For movement? I am a Lucio main so I move all kinds of crazy. For me to get better I used Lucio in the TRAINING GROUNDS lvl and set my jump to my mouse side buttons and just practice going all over without hitting the ground. Same could be done on any lvl alone. W,S,A,D, movement is key for Lucio to wallride in every direction without actually having to be looking where you are going.