The more sleep you get before your WBTB the better your chances. But of course if you get too much sleep before your WBTB you'll have a hard time returning to sleep. You have to do your own experimenting to find out the ideal length of time to stay awake before returning to sleep. If you fall asleep too quickly then stay up a little longer.

Since you're just starting out, understand that performing a WILD is entirely a mental process. The first thing you need to do is pay attention to how your own mind normally works while awake. Stay aware of your thought patterns and the different mindsets that you carry during the day. Then as you are trying to sleep pay attention to the changes in your thought patterns and mindset as you get more tired. With practice you'll be able to know how close you are to falling asleep by observing the changes in your mindset. You'll be able to watch yourself move closer and closer to sleep until you finally observe yourself actually falling asleep. When you've done this you've just performed a WILD.