Answer:
Just go to the bathroom before you go to bed and avoid drinking liquids before you go to sleep.
If that doesn't help, try a bed-wetting alarm. They really do work and are highly recommended by physicians. Below is a link to a Google document of a bed-wetting comparision chart. Just copy and paste the link into a new tab.
https://docs.google.com/open?id=0B2fRaGi9p40_N2E2MjM5MmEtOTVkMS00Mjg0LThkZjctNThmNDE2OTNjZmE0