CS

I tend to do better if I turn auto attack off not sure if you've tried that.

auto attack off, and only auto the minon when it gets low enough. Make sure your champ isn't too busy with attacking enemy at the time. Be patient and practice. Go into a custome game and practice cs'ing with your prefered adc for 10 mins. Than start a new game. You want to practice with low ad so you get the feel of how much it would do just by looking at the minon hp bar and estimating if your attack will finish it off.

Go into a custom and practice lasti hitting only with Anivia. I went through it and i cs alot better than when i started

Practice. Seriously, that's the only way you will get better.

Try attacking minions will full health twice, and when your minions have weakened the recently attacked ones, last hit those. Of course, while they are attacking one another, you can alternate your attacks between minions and allot your damage to each of them to maximize last hits.

wait until they are low before attacking

Make custom games with no bots or other players. Choose an ADC or your favorite champion with their standard runes, masteries, and starting items. Go to their meta lane and spend 10 minutes last hitting the creeps. Don't shove the wave by constantly using abilities or attacking full health minions, just wait for them to get low enough to die to one AA and last hit them (until they get under turret, then try to use whatever abilities you can to get them).

The benchmark for 10 minutes is 70 CS. Keep leaving the games at the 10 minute mark until you can get 70, then try bot games or normals while shooting for the same CS goals.

BONUS POINTS: While in these custom games, practice looking at your minimap every few seconds.

if you hold the s key you wont attack anything. stand in range of minions holding s until one is ready for a last hit, and shoot it