You don't need to concentrate on falling asleep, you just need to fall asleep like you normally do but while keeping the awareness, did you read the tutorial i linked you to?
Also what time are you WILDing at? If you are doing WILD at the time when you normally go to bed, then you are doing it wrong, best times to WILD are times after waking up(up to few hours) and naps. If you are already using those times though, try changing them around till you find the time at which you can fall asleep into REM easily enough.
Additionally you could try listening to something relaxing, like some relaxing music, white noise or binaural beats.