By far the best state of mind to have for a chess game is that of calm concentration. This means shutting out external thoughts and becoming one with the chess pieces for the duration of the game. Accordingly one must avoid distractions like the plague, both before and during the game.
Sometimes people think they should be ‘pumped up’ for chess in the way they might be for a boxing match, but this is simply wrong. Adrenaline is associated with a ‘fight or flight’ mode which is hardly conducive to good brain work or even the fine motor skills one needs to move those fiddly little pieces around the board.
Anyway, here’s a nice video on the subject for those who want to know more: