The lessons i learned when playing live
1. Don't try to 'compete' with anybody within the band volume-wise. The Total Mix is all important.
2. For those of us who don't have the luxury of an extra live sound mixer/ front of house man - keep your left hand on the volume slider (or use a volume pedal) and listen to your place in the overall sound. Dynamics is all important. Simple tricks like reducing vol during the verses and increasing it on the chorus and towards the climax does wonders to the energy level of the song.
3. Fill in the gaps, don't play in the same frequency band as the guitarist or bass player. Once again, your EARS are your most valuable asset.
4. Be prepared for an impromptu solo. NOW you can be loud.
5. Bring spare batteries, power cables, line cables, MIDI cables, sustain pedal and anything else you think can go wrong or missing. Also masking tape and torch are always in my gig bag.
6. Instead of hunting for sounds on your keyboard, put them in all in order of the setlist.
If you don't have a setlist or your band likes to play on the fly, then put the sounds in a 'bank' for easy search. If you're too lazy to do this, write down the location of your most used sounds and stick them where you can see it easily i.e on the keyboard. Make sure when the lights go out you can still see it.
7. Be creative - e.g. even in a 'metal' song, when there arent any obvious keyboards adding a 'choir' bed adds to the impact of the song.
8. Enjoy yourself and relax. It don't mean a thing if you arent enjoying it!