Remember, rockets fly off of your wings so you need to "aim" your wings and keep them in a straight line to your target. Any input of rudder, pitch, or yaw during a rocket run will change the course of the rockets if fired whilst inputting any of those adjustments. Anticipate your rocket run (think straight line at first), line up on your target well in advance and allow time for your aircraft to stabilize before firing.
After you have practiced the straight line firing of rockets and have that "sight picture" in your memory, you can begin to modify it with a bit of pitch, rudder, or yaw to achieve some creative results.
I am by no means a rocket expert.