You need to let yourself fall alseep without losing consciousness. This means you will actually fall asleep. Think of it in three steps.

1) Relax your body to an insane degree. Lots of people skip this, but its real important
2) Keep your brain active with some sort of task while you wait for your next REM period to begin.
3) Visualize yourself in a dream so you can detatch your consciousness from your body.

Its all about finding triks that work for you at each stage. You need a good relaxation technique, a good technique to keep your brain active, and a good dream entry technique. If you try a couple people's tutorials, you should find a few tricks that work for you.

It sounds like your WBTB was not quite long enough. If you were struggling to stay awake, you need to extend your WBTB time. Make sure you turn a light on, and do something like easy math problems or reading about lucid dreaming. You should not be groggy, but you should be tired.