All of these come from our gaggle of regular sequencers around here, and may be of varying usefulness. All these tips are worth keeping in mind, however. The Gunshot is NOT a percussion instrument. It is a sound effect. The Orchestra Hit is not a melodic instrument.
Different people use different sound cards, different synthesisers.
What sounds perfect on one may sound like absolute off-key garbage on another. Try to play a song on several different sound cards or synths and make any necessary adjustments before releasing it. In GM, percussion is set to channel 10, so it makes sense to put the percussion on track 10 when sequencing. Make drum rolls start quiet and get louder or start loud and get quieter. Don't keep them a constant volume.