1. Don't level your ulti after you hit level 6. Because if you level it after you hook someone (use ctrl + R for quick access) then the lightning will hit whoever you pulled. AND you don't accidentally steal cs from your ADC.
2. Hook fires from your right hand. It's not a big difference, but you you'll slide by minions more often on the right side than the left side.
3. If you're below D3, always, ALWAYS invade after buying items quickly. (I know this tip will be controversial) The zoning potential from warding deep early and having blitzcrank on your team makes your invades 9001 times scarier. Remember, you DON'T have to get greedy and try to get kills. Even a flash is worth it.
4. Save your ulti like a finisher early game. The lightning procs do more damage you think and you want to get as many procs as possible.
5. (A collection of small tips)

• Max Q, not W or E.
• Tear of Goddess is not as good as you think it is. It takes too long to build and you don't want either final builds.
• E is a AA reset. If the enemy doesn't have escape, hook -> AA -> E
• If your enemy adc DOES have an escape (ex. Trist W, Corki W) hook -> wait -> E. What the waiting period does is it cancels the enemy jump animation. Usually they will panic and jump away as soon as they regain the control over their champions, so wait.
• After you hook, try to move in front of the enemy. Even though the body block in LoL is not as great as HoTS, you will block some movement by the enemy.
• Don't exhaust right after you hook. Exhaust after they are out of your cc.
• As you go higher up in rank, you'll have more success from W -> running up to enemy -> E then Q.
• I see this mistake more often from lower elo, but ALWAYS look at the minion difference before hooking. If the enemy has more minions, even if you hook right, you'll end up losing the trade. So don't go too ham.