If your team has long-range crowd control such as 莫甘娜的Dark Binding, it can sometimes pay off to put points into Rocket GrabRocket Grab to greatly increase the damage, as well as a much-desired cooldown decrease.
When playing support Blitzcrank against a squishy botlane or a botlane with low CC, you can walk up to the enemy AD carry or support instead of initiating with Rocket GrabRocket Grab. This can be done by activating Overdrive and using Power FistPower Fist when you are in range of your target. Then when your target tries to escape, use Rocket GrabRocket Grab to pull the target back in. This is almost always a secure kill, or atleast a force of the enemy's summoner spells. When you do this, make sure your AD carry follows up. If your AD carry doesn't go in with you, you will most likely lose the trade and maybe even die.
Since Blitzcrank has trouble farming for gold, Aegis of the Legion can be used as a cheap and effective way to increase his survivability and usefulness to his team, especially if he's being built as a tanky-support role.
Against Blitzcrank Bots, it is also possible to avoid Rocket GrabRocket Grab by immediately moving sideways (that is, perpendicular to your previous line of motion) when you see the bot prepare to activate it. The same theory is true against human Blitzcrank players, but they are less predictable.
Champions that can poke well without putting themselves in much danger, such as Varus or Caitlyn are able to harass while being considerably safer from Rocket GrabRocket Grab than others.
When Blitzcrank goes for an unexpected grab, usually his allies are close by. Use this to your advantage and have teammates purposefully get pulled and have teamates follow the innitiate as usually the enemies swarm the person getting grabed.