An important part of the auditioning process is the initial application, which almost always requires recommendations from professionals with whom you have worked. Sites like Yaptracker have made this an easier process for both recommender and recommendee. It is not always possible to give the person whom you are asking to write a recommendation a lot of lead time, but when you can, do!!
The longer the lead time, the more in depth and thought out recommendation you will probably get. and as I have mentioned in other contexts, each thing that you do, is usually considered an indicator of how you do everything by those considering hiring you.