Not Updated For Current Season
I'm starting with condemn if i've going with somebody like Blitzcrank or LeBlanc for FB.
If solomid - then tumble for beginning and then focusing on tumble and silver bolts (or course learning ultimate when its possible).
i know the most popular tactics of last-hitting, but it works only if you much more powerful than your enemy. On mid lane for begginning i use another one. Its very simple - you must kill all minions as fast as you can, without skills. As a result you have all moneys from minions, your minions deal damage to tower, and your enemy cant get enought moneys because his tower kills some minions. In one wave of creeps its not important. but if 10 waves of creeps are fully farmed by you, and your minions instantly damages enemy tower its very helpful.
And of course you need to harras your enemy enought to don't let him farming creeps like you.
If everything ok, and nobody dies at most games i've destroying enemy tower until 10 minutes period ends. And what very important you can leave your line at any time for gang, shopping or regen.
At the late game you can try backdooring... if you choose right moment, you can destroy tower, kill enemy or two, and then destroy inhibitor. its very helpful if you are loosing.
You can decide what to buy and how to play only when you know vs what champ you will play.
Thats why i hate dudez crying "i'm on mid" in champ selection screen.
If there are high-ranged mage vs you, or stealth champ (eve, twitch) in enemy team, i prefer doran blade at start, and then vampiric scepter. At another look you can buy vampiric scepter first. It's very helpful if enemy goes harrasing you from first second. Say "hi" to Orianna, Karthus, Ezreal and other spell harrasers. They will just loose their mana for nothing.
The next tactics in itembuild is to get highest attack speed and something another. Berserker Boots and enemy cant just run out from you. The sword of divine, and you get armor penetration, and machinegun arbalet with pure 80-90 damage at every 4-th attack. At that time with maximised as possible "silver bolts" skill you will gain approximately that:
final hour + tumble 135+50 damage at first attack, then 135 with second, then 135+50+6% of enemy max health (60 vs 1200 health enemy) and fourth one - 135+(80 - 90 magic). = 785 damage with 4 attacks which are dealt in 3 seconds! and + 117 health vampired from enemy!
The fifth item you want is Angelic Armor. Let the Katarina, Katrhus, Caitlyn and others, who can do serous damage with their ult or last hits you, give you their lifes.
The last one item can be very variable. It probably can be Blodthirster, or Phantom Dancer for speed and crits, Warmhog armor for high health or Nashor Tooth for cooldown, but i prefer maldred bloodrazor. After that you can get baron in pair with one tank. Now you have 98 armor penetration, 2.3+ hits per second attack, more than 25% damage for 4 attacks and 250+ AD. only hard focusing can stop you.
Pros / Cons
this is almost "glass cannon" build which is great in teamfights and 1 vs 1. it can save you in many situations and correct your mistakes.
This build makes one very good and very bad at the same time thing - now your game is fully depends of your teammates.