Two techniques I use that work well are to not only clear your mind, but become intensely conscious of your present surroundings, and of yourself. For instance, try focusing awareness throughout your whole body, don't visualise anything, just feel. When working, or even just relaxing, try to focus more concretely on what you're doing at the time. This can be done even when oh, say, you're waiting in line at the grocery store.
One extremely good book on meditation I've found is The Power of Now by Eckhart Tolle. I was amazed when I first read it, I wondered for a moment if Tolle hadn't written the book specifically for JWs and exJWS. I kid you not, there's so much information in there that applies to us that it's not even funny!
For pure health, try researching books on chi kung or tai chi chuan. Although I've slacked off on it lately, I used to do regular chi kung and chakra work, and was much healthier then.