Let's get back on this topic which we had at least two times before.
I recently got into LDing again because...iono, I just got into it again and I wanna have one. I had two LDs so far, they weren't that spectacular.
Just to get you going;
A Lucid Dream is a dream in which the dreamer knows that he is dreaming and therefore gains unlimited power, the ability to do anything he wants. A dream is all inside your head and your head can alter it the way it wants, so if you have control over your head when dreaming, you can alter the dream accordingly. It's awesome, no limits, no bounds, do whatever the fuck you want.
Wikipedia Article on Lucid Dreaming, it's pretty good.
Big and great sorted-out community about Lucid Dreaming
Introduction to Lucid Dreaming
There are several ways to achieve a Lucid Dreams. Some people have them naturally a few times a month, or even several in one week. That is very rare though, while everyone can learn to have them. The most common technique would be the Dream Induced Lucid Dream (DILD).
It means that while dreaming, you notice you're dreaming. This either happens by chance, or by training. Essential are "Reality Checks", with which you check the reality (captain obvious strikes back). Those are things like looking at your hands, in a dream, they'll look odd, plugging your nose and trying to breathe, in a dream you'll still be able to breathe. Do these all the time in waking life, then theres a good chance you'll also do them in a dream.
Another, way more reliable but a lot harder to master way to achieve LDs is the Wake Induced Lucid Dream (WILD).
When WILDing, you try to "take over" your consciouseness from waking to dreaming while your body falls asleep. This works, but it's rather hard to learn. Still, it can give you a Lucid Dream just by wanting to have one.
Check out Dreamviews.com and look around the forums, I'm also active there.
ITT: Discuss Lucid Dreaming.