How To Choose Audition Monologues

The following is a list of points to consider when choosing a monologue. For a list of the types of monologues you should have and how to find them, visit Monologue Repertoire. This site also hosts a list of free monologues from plays .

Choose an audition monologue that have some sort of change in the character from beginning to end. This shows range of acting and an understanding of monologue beats.
Choose a monologue that is appropriate for your age range and life experience. Don't choose the monologue of a character you cannot identify with.
Choose a monologue that is appropriate for the show you are auditioning for. If you are auditioning for Shakespeare, don't use a contemporary monologue, and vice versa. If your audition for a musical requires a monologue, do you best to find a monologue from a musical.
Choose a monologue that interests you, with a subject that you either know about, or can at least identify with. If you find a monologue you really like but don't know enough about the subject, do some research.
Do not choose a monologue that requires an accent unless it is specifically asked for.
Make sure that you like your monologue. If you don't enjoy performing it, there's no point.
Either avoid choosing a monologue that is too long, or cut it down to size. Most audition monologues should be about one to two minutes in length. If the audition notice specifies that it must be of a certain length, time it very carefully several times and edit it if necessary. You do not want to lose a part because you didn't follow instructions. If you feel that you cannot edit a monologue to fit in the time allowed without taking out something important, choose a different monologue. There is no point in ripping a perfectly good monologue to bits just to make it fit.
It is okay to cut down and modify a script to create a monologue, but if you have made significant changes make sure to list it as an "adaptation".
Some 2-person scenes can be converted into a monologue by cutting out the other character's lines and modifying it slightly for content (the other character can be imagined and implied by your actions - it is an interesting effect). Never speak both characters' lines, as if you are having a conversation with yourself. This is not appreciated by audition panels. It tends to make you look a little crazy. :)
If you are auditioning for a stage part, use a monologue from a stage play. Do not use monologues from movies for a theatre audition.
Do not use monologues that were written as stand-alone monologues. I know those "free" monologues on the internet are very tempting, but most of them are very bad. There is a reason they are free. Monologues from plays have much more background to draw from to create a more complete character.
Do not perform a monologue in an audition without reading the play it is from.
Do not perform a monologue written by you or one of your friends. You are auditioning as a performer, not as a playwright.