iPhone or iPad Just Not Quite Right?

Don't forget that simply shutting it down, letting the screen go all the way to black, and then starting it back up again, cures a lot of what ails these things. In fact, it's a good habit to shut these things down and start them back up with some regularity... I'd say at least once per week.

It's also a good idea to plug in to iTunes and do a backup first - and every so often, just for good housekeeping.

As long as your backup is fresh, plugging in to iTunes and using the restore function should solve any lingering problems, but don't do this if your device is jailbroken and/or unlocked. There are ways to get these devices back to 100%, but if you are uncertain how to do that, you are best off being shown the first time.