Much of this will be redundant, but why not...

You could try staying up longer, and/or you could try getting in a more uncomfortable position, such as lying on your back. I would stay up longer or resolve not to fall asleep with more emphasis. The danger lies in not being able to sleep if you overdo it, and in my opinion this would be the worse scenario. You need to fall asleep in order to WILD, so it is better to rest and try again another time than to stew there for hours in frustration. Keep experimenting to find the right balance, and don't try too hard. Simply fall asleep with a confident intention to keep just enough awareness to get through to the other side.

The answer to your next question is a long one; so I suggest checking out some of the tutorials that explain this in detail. The short answer: don't worry because you can't miss it. Any number of sensations may or may not arise; if you are using imagery, then the images will become realistic and you can enter the dream. If you are not using images, ultimately you will feel a "shift" after which you can just get up into the dream.

Usually if I use images it is smooth, but if I am not I usually get vibrations and static noise in my ear, from there I can get up or wait until I float. This is an oversimplification, as you can enter in any combination of ways really. You can use images and then cancel or banish them; likewise you can enter directly and then create a dream scene as you enter. Just know that if you try too stubbornly to hold on to your awareness you will not fall asleep. Err on the side of sleep every time and your practice may be more successful, or at least less frustrating.