Here's what I did to get good at CSing, which a high elo friend taught me.
- Take off all of your runes and masteries
- Custom game with no bots
- Choose a random champion, they all have different attack speeds, base attack damages, and attack animations
Edit: Do not use any spells or level up any of them with passives
- Do not buy ANY items
- Your goal is to hit 60-70 CS by 10 minutes, if you miss out on your goal, recreate the game
- If you hit 60~ CS @ 10 minutes, try to shoot for 120@20 minutes, this is standard CS for high elo games, if not low.
Practice this for 30 minutes a day, preferably before you start playing actual matches; I almost always do a practice round at the start of the day before ranked. It takes some time to kick in, but it will definitely be there once you get into a game.
The purpose of no runes/masteries/items/random champion is to get you GOOD at CS, if you can do it without any of these, you can do it much better with them (And after enough practice with that random champion button, you'll be able to do it on almost any champion).
Hope this helped, GLHF