Get In The Piece Before You Start
I try to have a mental musical cue for every excerpt that will allow me to start immediately in the correct style and tempo. For example, in Bolero I try to hear a few steady bars of the snare drum rhythm before I jump into the excerpt. In Ein Heldenleben, I also try to hear a few bars of the snare drum. In Tuba Mirum and Hungarian March I think of the tempo at which I want to play the eighth notes in the later parts of those particular excerpts in my mind before I start. Until I feel comfortable with the established style and tempo in my head, I don't begin the excerpts. Starting before you reach that comfort level can be a recipe for disaster. If you start off unsure and it takes two or three bars for you to get into the feel of the piece, you've already lost the battle and the attention of the committee/audience.