I tried several Android softwares to manage my running apps, but only one seems to be efficient, and that's called Advanced Task Killer or ATK. It can be highly customized (what apps to kill and/or not), it has a very easy to use interface, even for new users, and it has different levels of using.
One of the most commun problem for using this app is related to its predefined Auto Kill levels: Safe, Aggressive and Crazy. So, what's the purpose of these levels:
- Safe (most recommended) - it's killing apps that are not running but still consuming RAM;
- Aggressvie - it kills apps that are not running and background running apps (I'm using this option, but highly customized);
- Crazy (not recommended for beginners) - it kills all apps that are not started and used by you.
Of course, you could not use the Auto Kill function if you don't want, but in that case you need to check each app and setup it when to kill or keep alive it. Anyway, to avoid any troubles for using ATK, you should keep it as simple as possible, without trying to highly customize it (except the case you're an android programmer).