Imperfected
Member
Make a custom game with no opponents or bots, go into lane, and concentrate on only last-hitting. Don't hit minions at all unless it's to last-hit them; press 'S' (by default) to stop your auto-attacks while you're waiting. Use only auto-attacks to finish them off at first.
You should notice that normal minion-vs-minion damage creates spacings where it isn't possible to finish all of them off (either because of minions going down near-simultaneously or, particularly in cannon waves, because minions lose too much health to be reliably last-hit with an auto-attack). This is where you want to start practicing weaving in your activated abilities to pick up what would otherwise be lost CS.
Before you end the custom game, make sure to find a lane where minions are pushing into a tower in a large group. (This will happen naturally at some point in empty lanes.) Take some time to get used to last-hitting under tower. (The general rule is: an undamaged normal melee minion can take two tower shots before you need to last-hit it. A normal ranged minion can take only one before you need to last-hit it, so you either need to have enough damage to finish it off from there or "prep" it by doing one auto-attack before it takes the tower shot.)
After that, just play games, honestly. You don't want to spend too much time on "drills"/fundamentals, because you're going to need to start learning to CS under duress ASAP. It's sort of like free-throw drills in basketball.
Edit: Gambit gives up a dragon solely due to lack of vision, Origen gives up a baron solely due to lack of vision. I am disappoint, EU, even with my low expectations.
