For the love of all that is good don't use any kind of task killer.
Like already mention, turn down your brightness. On most phones that's the number one killer of battery. If you go into settings>about phone>battery use, it will break it down for you what uses the most battery. Just looking at mine, the display is 84% then its Android System at 7%.
Besides brightness, turn off bluetooth and wifi if you're not using it. On some phones I've noticed that Cell Standby is sometimes the highest battery drainer, that usually happens if you're switching constantly between edge and 3g or looking for a signal. Also, if your phone and/or battery gets hot, it will also drain faster.