One quick thing before we start — 99.9% of the time it is not actually iOS that is causing your battery to drain quickly. I guarantee you that if you erased your phone and there were no apps or email on it, it would last for ages. But, no one uses their device like that, nor should they. Hopefully with these steps you will be living in iOS battery bliss while still using all the apps and features you love.
There seems to be a lot of urban legends as to how to make your iPhone battery last longer. This is from a former Apple Store Genius it so he/she has probably seen it all. This is about as definitive a piece I've seen on this subject. Great article.