warm ups and performance
these are the strategies i have used over the years that i find most helpful.
don't over-play the night before. do a nice slow warm up, don't go too far up in the register. play long tones. after you're wrm, play some of those relaxing pedal tones to get the air going... then play a few more notes, higher up this time, and then stop. you really don't want to wear yourself out the night before a performance/audition.
the time you have to warm up before you recite depends on the situation. you should be able to have a perfectly adequate warm up within about ten minutes.
start with decending lip slurs: Bb-f-Bb, (start on C for treble euph) A-E-A, and down, and then come back up. then do a few ascending lip slurs, using the same pattern.
pick an easy note, concert F for instance, and play a nice round mezzoforte on it for a few beats. then go to mp, p, pp, back up to mp, all the way through a full (but not blatty!) fortissimo.
take the same note. play different articulations: legato, marcato, fast rhythms, slow rhythms... use the same excercise on a different note, maybe a concert Bb....
warm up to some of the higher notes. slowly make your way up to a high Bb. then come right back down and play some of those soothing lower notes.
your warmup is now basically complete. you may want to play a few tunes, but don't get into the mind set "if i play this scale just a few more times it will be perfect!"
if you still have to wait awhile before you play, it is a good idea to buzz. this keeps you warm but not too tired, and it doesn't (normally) disturb others.
try to avoid carbonated drinks beforehand. drink juice or, even better, water. eat healthy foods... if possible, see if you can bring a water bottle into your performance/audition. this is good for when you get a dry throat.