This is my first guide ever so please be easy on me with the details and writing.
I've mostly always played with Blitzcrank, And I have always had a positive score with him.
This build with guarantee a great score if you follow this guide. I hope you like it, In this build you have everything, DPS and Survivability.

I go 9x armor Pen, 9x .41 Mana Regen/5 Sec, 9x .65% CDR and 2x 3.33 Armor Pen and 1x 1.89 Magic Pen. You can always mix it up, But this is my preference.

I've tried many different masteries, and This is the best one I've done yet 21/7/1. The 1 in utility goes for Ghost.

The items I selected are best for all around everything, You get great HP and Mana Regen, Good DPS and Great survivability. Its pretty standard hybrid/dps, Ive never seen a hybrid Blitzcrank, Its always a Tanky AP. For the last item depending on who your facing.
You can either go with Atmas Impaler for DPS oriented team or Force of nature for Caster oriented team.

The way you wanted to play blitz early game is last hitting minions, staying defensive.
Your should always be the one to initiate when to attack a enemy, Hiding in the bush is always good, so you can get your pull and take the kill.
If they are ranged and pushing real hard, You can always hug tower. Make sure there are little minions, Pull the enemy, hit them with you E and that should be a kill right there.
Blitzcrank is one of the at laning by himself.

This is an absolutely great build, I really recommended. You will be unstoppable, I've always done great with this. I always appreciate criticism and comments to see suggestions, always welcomed. This is my first build/guide, Ill try to make it better in the future, with pictures and everything but for now, This is the basics.