Where as top lane is about tankiness, sustainability, and controlling your minions, mid is typically more fast passed, as the distance between towers is so much smaller, so damage is a bit more importamt. Mages like Annie and Ziggs are used here because they tend to do the most amount of damage to the minions for the least amount of mana. Assassins like Zed and Katrina are also used because....well, they just murder the shit out of mages.
Then of course, you have to fight your lane opponent as well as CSing. Mana and cooldown management is so much more important though because after a failed burst or when your too low on mana, you'll be defenseless to a counter attack. All the while, you want to keep killing minions.
Now for ganks. Be paranoid. Including the spots on by the enemy turret, there are 6 different places for the enemy jungler to show up to kill you, and because you're most likely a squishy, you will die if you get caught in the 1v2. People still don't do this, but be sure to ward and pay attention to your minimap. If you know for sure the jungler isn't after you, then you can focus on other things.
Generally, mid laners will recall back to base by level 5, even when ahead. By that point, they'll be low on mana, and maybe health too. When one mid laner does this, the other will want to too so they can get their items too. And because mid is such a short travel, they can afford to do this. Since mid laners are typically bursty, this this return and the following level up to 6, will be when you feel your first power spike.
Just some generic details. Not sure if it's too helpful.
