This is my first build on mobafire. Blitzcrank is a really good champ, who can deal large amounts of damage if built right. I suggest rushing rod of ages to make you not squishy, since you are a melee caster. If the enemy team has alot of stuns/slows, don't get sorcerers boots, get merc treads. This will make you almost impossible to stop while overdrive is active. The last item I recommend was a guardian angels, this is just in case of death. If your facing mostly ad champs, I would recommend thormail instead.

Magic penetration runes explain themselves. More damage and more worth it then AP runes.

Blitz burns through mana early game, so the more regen the better.

Cooldown reduction runes help you with the grabs and to spam e.

Pretty self explanatory if you have ever played blitz.

ROD OF AGES: Makes you more tanky, and gives you AP and mana. Overtime it pays off.

Boots: Go with sorcerers unless your getting slowed, stunned, or rooted a lot. (Mercury Treads)

Lich Bane: Gives you that great pow after you pull them in.

Archangels: Mana, which makes your passive OP.

Rabadons: More AP, more damage.

Armor: To make you more tanky, if you don't know what to get, just go for guardian angel.

You want your pull first, its the most important part about Blizcrank.
Then you want your knock up, so you can pull em in and knock em up.
Overdrive, its nice to have ready.
Max out your knock up first, so you can constantly knock kids up.
Overdrive so you can get out fast.
Your ults passive does most of your damage, and use the burst to finish them off.

This is what you gotta do,

Try getting a solo top lane, so you can lvl up fastest. Plus people tend to be stupid when 2v1.

Try to pull them into the tower, knock them up, and exhaust them. If they are dumb enough to get that close. Try to turret hug.

If your in a 2v2 lane, just focus one champ and keep pulling them into both of you and dealing damage. Use ult to burst damage for the kill.

Thats pretty much it.