I've never tried this, but a common trick among lucid dreamers while they're training themselves is to drink a lot of water before bed. The idea behind this is

I've never tried this, but a common trick among lucid dreamers while they're training themselves is to drink a lot of water before bed. The idea behind this is to associate the feeling of needing to pee with dreaming. So any time you feel like you need to use a bathroom, do a reality check to see if you're awake or not.