Hello Kitten,
The Rocketeer is one of my favorite and most played mechs.
It gets a lot of hate from both ends:
Some call it over-powered because it annoys them on open maps like Bunker.
Some call it under-powered because the turret mode is utterly useless and it's splash damage and close range are a huge detriment.
In truth, it needs a little TLC. Especially because the former development team was trying to tweak the Hellfires (lock-ons) - they started by nerfing them way down to where they barely track and fly slowly... and were going to slowly build them back up until they found a sweet spot. Then, Adhesive collapsed and nothing more was ever done to the Rocketeer.
However, I've still figured out how to make it work really well for me.
First: Turret Mode = Suicide Mode (except in very rare circumstances)
Second: Do not expect to be an assault mech. Learn it's effective distances and use it as a suppression weapon - keeping the enemy held back from points of interest. There are plenty of good spots on most of the maps where you can poise your Rocky, making it easy to pop in & out out of cover to lock-on quick, fire and duck behind cover again.
Third: Learn the art of the offensive retreat. Rocky is very good at specific distances (map and obstacle dependent), and keeping that distance is critical to maintaining suppression and staying alive. If you learn to know when to start backing away from an approaching enemy and time your firing, you'll find that your opponents either die trying to get close enough to finish you or, the smart ones, realize they need to give up on getting you and go elsewhere.
As for other tips:
Don't stay in one place for very long. Once you've annoyed enough people, they're going to be on a witch hunt. Better to move to a new location, preferably with a good view of your old location - and start the cycle of annoyance over again.
A lot of people will tell me I'm wrong, but I like to equip my Rocketeer with an A/C (air dodge). When the enemy gets uncomfortably close, I find it surprises the heck out of them when I suddenly go airborne and start strafing in the air (while offfensively retreating)... blasting them with unlocked Hellfires raining down from above. I get more kills that way...