Will Power
When it comes to lucid dreaming Will Power is everything. When you go in you must be confident - you must grab the content. And once you grab the content you can't let go. The sleep state is intended to knock out your conscious mental state.
What you will be doing is swimming against the current. Imagine that.
To be successful, have an intention going in. Know what you want to do when you get in there. Will you fly? Will you go swim with mermaids? Will you capture stars?
Whatever it is, stick with it and never let it go. Stay strong in your mind and in your intention, no matter what.
“Great heart will not be denied” -J.R.R Tolkien