Try to achieve a good balance in your selection of songs.
Think about your audience in advance and select a theme that might appeal to it.
Play to your audience, but also please yourself. The audience is more likely to respond well if you are enjoying the performance.
Build your program around a song that you selected as being the most meaningful or dramatic.
Create a mood that builds up and leads into that pivotal song.
Work back gently onto a lighter mood after that climax. Avoid jerking the audience out of an emotion you've worked so hard to create.
Visit the place where you are to perform. Have a good look around.
Walk from the dressing room to the stage and back and eliminate any hazards you might meet when entering the stage.
Check out the acoustics in advance in case you have no time for a rehearsal.
Check for blind spots and locate the best position for yourself.
Work with your accompanist - if you have one - to make sure he or she can hear you and vice versa.
Make sure you will be getting enough performance space.
Check the proper dress code for every performance.
Be careful about your use of color. For instance, your pink dress might not go well with the bright orange curtains of the theater. A blunder in this area can be extremely distracting to your audience!