Possible Duplicate:
How can I stop applications and services from running?
As I can't uninstall certain programs that come with a phone (My case HTC Desire (not rooted)) how can I prevent certain apps from launching or trying to sync? And hide them? Or "Auto-Kill" kill them
For example
For apps that sync, any app with an ounce of politeness will have any entry on the Accounts & Sync page in Settings where you can disable syncing. This is certainly true of the official Facebook and Twitter apps.
1) Consider rooting your device, it's really easy now with the Unrevoked package
2) Settings -> accounts & sync. Here you can set options around what does it doesn't auto sync
Autostarts allows you to view which apps receive which events and edit them so that you can prevent certain apps from receiving problematic events (the ones that keep restarting the app). As far as I know it won't help with some low-level apps that run all the time and restart themselves with no events occurring at all, but it should help with others.
There is also an app called startup cleaner. I found it useful in preventing some apps from starting.
With the Samsung Galaxy SIII running Android 4 (and generally starting with Ice Cream Sandwich), it is possible to disable (some) pre-installed system apps without rooting the phone. I'm still going to root it, I think; factory apps imposed upon me which cannot be disabled or uninstalled basically creep me out, quite frankly. If nothing else, it's just...rude.
Starting with ICS (Android 4.0), you can simply "freeze" bloatware you don't need. This means, you make them "unavailable" (or rather "un-executable") on your device -- which makes them invisible in the launcher, and stops them from being started in any way -- while being able to "unfreeze" them any time you feel the need. No root required anymore.
If you're not yet running ICS -- no way to really stop that without rooting your device. Then you have the choice to freeze or even completely remove the crap, e.g. with the excellent Titanium Backup -- which, as a "side-effect" (lol) gives you the possibility to make complete backups of all apps and their settings, and that even scheduled. And for cloud-lovers, TB has support for Dropbox built in as well...
Other non-root solutions are only half-hearted: Without root, you cannot uninstall the pre-loaded bloat, and you cannot stop it from being autmatically launched (yeah, some apps promise they can -- but they are just shooting them as soon as they start, so im some cases they start again and get shot again and... you don't want that. The only decent solution in this group I know of might be Autorun Manager which, in non-root mode, detects such "restarters" and then ignores them. In root-mode it also allows to disable listeners to really prevent apps from auto-starting -- which might be nice if you want to keep the app for rare uses, but do not want it to run automatically).
EDIT: Beware that rooting the device might void your warranty -- and removing system apps (wometimes already generally modifying the /system partition, which is also done by "rooting" as it must place the su and superuser.apk there) might prevent future "official OTA updates", as those often check the CRC sum of the system partition -- which no longer matches after altering its content. This all does not apply to the "Freeze" of apps, of course -- at least not to the official ICS variant of it.
To remove bloat ware, rooting the phone and install titanium backup.
You can also consider an App Manager such as Advanced Task Manager that allows you to kill running apps. Also handy when you have opened a number of apps and they stay open in the background. Simply select and push 'kill'.
Most apps that runs in background should have a setting to disable background updates or something similar. If they don't, then just uninstall them and find an alternative app that are more acceptable. Alternatively, you usually can ask the developer; if the apps are any good then they would have a good development team that listens to their users.
Otherwise, I don't think there is any way to prevent apps from starting. There are several task killer apps that allow you to kill apps if they start; but without rooting or installing custom ROMs, I don't know if it's possible to prevent them from starting in the first place and still able to use the app when you need to.
You have to uninstall them.
Android apps are able to register with the underlying Android system to receive certain events and service requests, and the system knows to start the app up if those events or service requests come in.
Unlike on a standard desktop apps "running" on Android are often not actually running at all (they are blocked until an event or update occurs ... or to refresh state from the network). In general, Android apps are much simpler to suspend and resume than desktop apps, so the system can swap them out if the CPU or memory are necessary for another app without much complication. So, other than having a clean list of running apps, there isn't much to be gained by killing apps.
That said, if a specific app is behaving badly and using too much CPU for the value you get from it, then uninstall it and/or ask the developer to fix their badly behaving app. But really, if the app doesn't show up on the 'battery usage' meter, then you don't really have anything to worry about.
See this question for some answers for more specific apps.
