Oh dear, now you're asking the hard questions. I use the Task Killer app. Despite the bad raps I've read about them, they've always worked fine for me and help control my applications.
I haven't learned the Droids well-enough yet to tell you exactly how I do it (hopefully an expert will jump in here to save me???), but I normally just spend alot of time clicking and clicking and clicking around through all the menus and options and settings and make changes. I can't remember where I found the options to hide various apps, but I've come across the option to do that in my wanderings around the mysterious Droid universe.
I also go into the application settings for management, uninstall options, force closures, etc. etc. Whatever I can find that seems to help save the battery power is what I play with until I get my settings to suit my fancy.
I'm sorry I can't be more specific. I normally learn by clicking around and digging into the system, but I can't always remember exactly how to tell you what I did.
Hopefully some other experts will jump in here to guide you better than I can.