I Agree with The Blackening, very good post.
Read it!
What has helped me most get very good at CS is :
A. Watch the minions attack each other. Find the sweet spot, and attack before the next minion attack. This way you can last hit a minion even if all 5 of yours are attacking a single minion. You get a feel of when their attacks will land, and estimate when yours will get the lasthit.
B. Learn to hit minions at tower, with above statements, (ie 1 hit from tower for ranged, 2 hits from tower for melee) Unless you have no items, then the rule is hit each one once, and wait for above (1 hit for caster, 2 for melee) and another auto attack for last hit.
C. At each wave, check the map. In between a wave or mini wave (from melee minions to when your minions move to their caster minions) check the map.
D. Use the S button to stop or stand still. This stops your auto attack animaiton, so if you accidentally begin an attack at the wrong time, S, stop, and wait a few more half-seconds, attack again. Great for estimating the sweet spot 
E. Check your map after each lasthit.
F. Check your map after each lasthit.
F.2. Check it again. And call out mias you see.
G. Dodge those skill shots =p