What helped and helps me, is closing my eyes. No visual distractions and just focusing on playing. What also helps is reminding myself 'i can do this'. If you've rehearsed and you can pull it off in the practice room, you can do it live too. Before a gig i do a warm up so i'm ready at the go, make sure i'm sitting relaxed and that the setup (especially with house kits) is comfortable.
Regarding setup up... take your entire set apart and start building it up. Begin with the bassdrum + pedal. Move in your snare and position it so it's comfortable. Next your hi-hat and adjust the height etc. so it's on a comfortable height. Play a beat for a few minutes and adjust what you feel needs adjusting. Bring in the tom(s) and floor tom, again adjust. Then bring in the ride, again adjust, play some beats etc.
If you take your own set to a gig, a carpet or rug with everything marked on it is a huge help!