I usually lay on my back. I have tried it in my normal sleeping position (on the side and my stomach) and nothing has happened in both positions. Oh and another thing:Does streching really help before you attempt a WILD. I start in my legs and go all they way up to my forehead but after like 30 minutes of just laying there waiting for HI to start I get bored. My Dream Recall has gotten alot better though! Anty tips?
It’s best to do it on your back because if you do try it in your normal position, you might fall asleep, or at least that’s my reasoning.
And yes, you should stretch every muscles in your body because this will relax you.
Both of the times that I went into SP I was laying flat on my back.
As for the stretching question, having all your muscles relaxed is a good thing, but be careful not to concentrate too hard on relaxing all the different muscles separately (like I did: “Okay…relax my toes…relax my calves…relax my thigh muscles…relax my stomach…”, etc.) because then you are concentrating fairly hard and not really allowing your brain to relax, even if your body may be.
I recommend you do a search on Silva Ultra Mind and link to the free program. If you actually do it I think you will find you can relax easily and start HI quickly. You may find it enriches other portions of your life as well.
What really gets me relaxed is going to be after a really hard day on the wrestling mats. You get really tired. Also, techno music, for some reason, helps me.
try not to focus to much on wanting to lucid dream to much, your mind makes sure that your body is asleep (body being your conscious mind? i dont know but whatever) befor starting dreams otherwise you might act out your dreams. anyway try telling yourself “im going to remmeber my dream” insted of “1 im dreaming 2 im dreaming” because the counting might make you to alert and your mind might just pick up on you saying “1 im dreaming” thus knowing that your body isnt asleep
also i try to lay on my back when i try WILD however i get the best sleeping positions when i dont have lucid dreaming in my head 
so that isnt easy to get to