Killing tasks actually negatively affects battery performance and is not recommended (unless they are acting up). Android is optimized to run at or near memory capacity. When it has too much free memory, it will load an app in the background (using processor power and hence the battery hit). If it doesn't have enough memory to open an app you want, it will close an app that you infrequently use. After a while, it will only load apps in the background that you actually use.
Other general battery saving tips are controlling syncing. I do not need my Facebook synced in real time, I am OK with it getting new info when I open the app. Most apps that sync have an option to disable or control the frequency of their syncing. Tailor them to fit your needs.
Check the battery usage stats (Settings | About Phone | Battery) and check to see what is using the battery. The top two are usually Screen and Android OS. Your Android OS may be higher than others see due to the task killer issue I mentioned above. Beyond these two, you can look for other apps that may be eating your battery.
I hope this helps.