A lot of people suggest reading On Writing by Stephen King. I personally didn't find this book all that helpful--that isn't exactly right. There were helpful tidbits scattered throughout, but overall I think you could save yourself some time (listening to King toot his own horn). The two things I thought were the best part of King's On Writing:
1) If you spend an hour writing, spend ten hours editing.
2) 99% of what you write is crap.
3) Write 2,000 words a day.
And I'm even a little iffy on the third one. I can see how it would be useful to new writers (as it was to me years ago) but the more experienced you get, the less I think that is possible for some. Some people can and do write 5,000 + words a day, and they feel comfortable about that. I'm not one of those people. Some days I write 200 words, some days I write 10,000. For me it's just about writing SOMETHING every day.
One book I would recommend, though, is Zen and the Art of Writing by Ray Bradbury. His techniques are useful, but it is more than that. While reading this book I get INSPIRED to write--I get the URGE to write. It's the only on writing book that has ever done that for me.