I'd say that you need to send yourself into a deeper relaxation, almost a meditative state, when attempting to WILD. As stated previously by Looke, you should try to get yourself into a more comfortable position, this doesn't necessarily mean you have to get into your sleeping position per se, just one that will allow for a nice amount of relaxation of muscles, so that you are limiting tension within your body. Also, relax your mind as well! If you're lying there boosting your brain activity trying to relax your muscles and get completely comfortable, your only being counter-productive.

Additionally, In regards to what Gab said, it's much easier to attain a WILD through a WBTB method as well, if you want the best, most easily obtained results. Though it is most definitely possible to achieve a lucid dream through WILDing without using WBTB. Furthermore, If you feel as though your results are lacking while your attempting and practising WILDing, I recommend switching it up a bit! WILD isn't the golden technique that works for everyone, everyone is different. Test out some other methods/techniques to attain lucidity, and see how it goes.