My name is Sir Sagrell and I am currently Platinum IV on eune. I have 94% winrate with Blitzcrank in 17 games and I am a very experienced player. I have played over 400 games in dota with Pudge (the similar champ with blitz) and also hundreds of games of blitz over the past 3 years. I hope you find this guide usefull.

Be as aggressive as possible. Hook any one (exception when laning against Soraka you should be hooking her most of the time). Don't worry about hooking support not even when it's a big tank like Leona or Alistar, your adc has time to back off and decide whether he fights or defends you thanks to your E knock-up. This way you will always get something off the hook. Either you do damage to support/adc or you actually get a kill. Aim to use ignite BEFORE enemy adc heals (smart stuff). With the tanky masteries and runes you should be able to overextend quite a bit and not die (passive shield helps).

Just as laning. When you are around teammates you can be as agressive as possible. Just don't stop. Hook any non-tank champ (or even tanks IF YOU ARE AHEAD AS A TEAM). Aim to use your ult to damage as many people as possible. Don't be greedy with W and E. Use them as often as possible.

Practice hooks as much as possible. This is your sole purpose, get people out of position and punish them! The key is practicing until you can land most hooks and outplay the enemy mentally. There is no real way of teaching this, you need to feel the enemy and read his movement.