Make sure that none of the sounds are clipping ("going into the red") on the output mixer. By default, RMS Keyboards is mixed to an appropriate level, but if you are adjusting the mixer settings be sure to keep an eye out for this. If you need more volume, try turning up the gain or volume on your mixer or amp.
Set up the computer in the pit so that it is within easy reach and the screen is visible from where you will be sitting. It is very useful to reference the Current Setups window while you use RMS Keyboards. Also, place the computer on a sturdy surface - a small table with a no-slip surface is an excellent idea.
Do a full sound-check with RMS Keyboards before each and every rehearsal or performance. This will eliminate any nasty surprises, like starting up the Overture only to find that someone's turned off the power to your speakers! Doing a complete sound-check well in advance of each rehearsal or performance (i.e. not five minutes before the curtain rises) is our number 1 tip for avoiding last-minute problems and stress.