Oky Doky first off let me explain the brilliant reason im doing this: I'm bored (and of course im a nice guy )
Also if there's anything incorrect, inaccurate or if you want to add another "way to fail", I hereby allow you to post .

Anyhu, lets get started.

Way No.1: Not being relaxed/Being stressed.
If you've had a hard days work or just have something on your mind, nagging at you, then its probably a good idea to try solve the problem, or if not possible, try spend more time in the relaxation stage before attempting a WILD. Reason is: your not going to be able to get a good or constant level of concentration, which, of course, is needed to enter the later stages of a WILD.

Way No.2: Talking to yourself(in your head).
Again this falls under the category of concentrating; the mind needs to be almost blank to enter the deep stages. To achieve this, use techniques like concentrating on your breathing or an object in your head. You'll find that concentrating on one thing for a period of time is actually much harder than it sounds. Having said you should concentrate, I have to warn you not to over-concentrate(ie. Putting all your efforts and mindpower into the task) as this can prohibit you from falling asleep. From all the resources on WILDs I have read on the internet, not one has ever specifically mentioned this, resulting in me staying awake for up to 60-80 minutes before(Silly me). Do try concentrate but also try to relax on the effort if that makes sense.

Way No.3: Fear.
Fear is probably the most common cause of a failed WILD attempt. Even though you've probably heard people telling newer members that there's no reason to be afraid, they too were probably afraid at first. I was startled and afraid the first time too. It's a new experience and you have to get used to it. But trust me, if you can shake away that fear(which will shake itself away anyway after a few times anyway) it should be a fun ride through the vibrations. Theres absoloutely nothing solid behind the fear, its just a fear of the unknown.

Way No.4: Using a technique that doesn't suit you.
When I was starting WILDs I made the mistake of using techniques that weren't suited towards me. For example I used to use a technique involving focusing on hypnagogic imagery when I could never even see hypnagogic imagery. In fact I've never seen hypnagogic imagery or experienced sleep paralysis for that matter to this date! And yeah, I know...Im weird. I know it's harder than it sounds, but try to find a technique that suits you.

Way No.5: Having a distracting environment.
I don't remember how many times I've been trying to WILD when my little brother or sister run into my room and start pounding me silly(I know they love me) or when a football suddenly bangs off my window and jolts me awake. Try to choose a time where you wont be disturbed during your attempt, and maybe don't attempt if there is a good chance you will be distracted or woken as it may frustrate you. Also as a subnote, make sure your not hungry, thirsty or need to go to the toilet before you attempt.

I'm sure there's more but I'm in a hurry to go to my summer house in a minute or so, so good luck and have a nice summer.

Cya soon.