This is the realm of adventure...when you can wrestle control from your
sub-concious, this is the ultimate form of
role playing. If you have ever wanted to discuss
foriegn affairs with your
Great Aunt, in the middle of a
WW2 battle field, this is the way to fulfill that
twisted desire.
The trick to having a lucid dream is 3 fold.
1.) You must be willing to question reality, that is, you have to ask yourself, "what really is the difference between the waking world, and the dreaming one?" Once you find the answer, you can test the waking world constantly to find those clues that tell you you're really awake.
Look at a piece of writing, then look away, and back again. If the writing changes, you're dreaming.
Try and float off the ground. Don't just pay it lip service, actually see yourself floating off the ground into the air.
Review the events of your day, as often as you can. Usually this will become habit, and once in a dream the glaring inconsistancies in the dream will elucidate your conciousness.
2.) Work with your sub-concious, in as many ways possible.
You need to, on a very regular basis, allow your sub-concious to play, and/or communicate with you. This can be as simple as alotting some day dreaming time (your favorite method will usually suffice).
It can also mean that your sub-concious will forceably take back control of your dream, insisting on it's will being done (don't worry, this means that there's a message it really wants to share, and believe me, if it wants to share it, you have no choice).
3.) Paying attention to what your dreams are telling you.
A dream diary is good for this, as your dreams will follow a pattern which may not be obvious in any single episode. If you work enough with your dreams, your sub-concious will stop having to frantically fill every sleeping minute with urgent messages.
This also will help you have more fun with your dreams (have you ever had a nightmare? ever wish you could change the ending? never have the dream again?).
Or, if you lean toward an esoteric vein, lucid dreaming is the gateway to Astral projection, or out of body experiences. In fact, some sources suggest that a flying dream is really a unconcious OBE, and taking control would initiate full blown projection (some say it's the other way around, that lucid dreaming is just a watered down OBE).
One thing is for sure though, you will never think of sleeping as wasted time again.