Do not miss your grabs. Do not grab their tank or initiator. Use your judgement to grab when the time is right. Use your grab to pick off their carry or mage, so you have the team fight advantage. If you grab a squishy target, chances are, it will be instagib'd.

You will support ONLY in the early game, by buying wards if needed and by offering kills to your lane partner. GP10 is mendatory, as it will be your ONLY source of revenue. GP10 is not to be taken lightly, it will give you a LOT of money, in addition to the kills you will be getting. You will become very tanky late game, able to support your team with your skills and initiating power.

The reason you buy instantly your items after your trinity force is your GP10. The longer you wait with your GP10, the more money you will have. If you sell it, you will have less income, meaning slower items. Of course, late game you will be able to farm a little, but GP10 is your primary source of revenue for a LONG time.

Max q for cooldown and early damage. More grab = more kills. Max W second, you have to be able to chase after opponents, and because blitzcrank has a very low base movement speed. Max E last, because you only get lower cooldown, and you most likely will grab before using it, and grab's cooldown is much longer then power fist. Ult whenever, because that's how you're supposed to roll.