Hm I usually have the same problem, and so I figure that the best visualisation would be something that incorperates as many senses as possible...

Here's one for ya:
Imagine you are walking down a beach. You can hear the waves rolling in in a soft steady rythm (in time with your breathing maybe). You pause and look out to sea, and see the way the ocean glints in the sunlight, and you feel a slight breeze. You take a deep breath of the wet, salty air and decide to take off your shoes.

Leaving your shoes in the sand behing you you run along the beach, feeling the warm sun on your skin and the sand between your toes - it's so calm and quiet that you decide to yell out, you're all alone and no-one could possibly hear you. You yell out and run around for a bit and do a few cartwheels.

It feels so good, and you feel all your stress just draining from you. After a while you start walking again, letting the wash of the sea tickle your feet for a while. You find some rockpools and dangle your feet in there, looking around and exploring to see waht you can find (this shouuld be good for your imagery, just let yourself explore). You walk along the beach and explore the seaweed, finding peices of driftwood etc (again, let your mind wander a little bit). Eventually you move a piece of seaweed aside... underneath you find a funny looking piece of wood. What is it?

You dust off some more sand... it looks like a chest! You start digging around the chest, digging and digging until finally you lift it out. What could be inside? (all the while make the visuals as detailed as possible - see the grains in the wood, the rust on the metal etc)
You flip the catch and slowly open it...

Now you can put anything inside the chest - a key, something to use, even maybe a piece of paper saying "YOU ARE LUCID" or something. Maybe it is something with special powers to make you fly... use it, explore with it...

Hopefully this might help you, I never really have used it much yet, but now I have written it out I might try it again. Yeah it's a bit corny, and like every meditation tape out there, but the key is that the sand and the wind help you experience everything so much better... i guess the key is in the details. If ur mind wanders off a little bit, bring it back by thinking of sand between ur toes....

hope it helps