If you have a new 3G iPhone, or if you upgraded your old iPhone to the new 2.0 software, then here are some tips to minimize problems. First, don’t download apps directly to the phone. If you have done this and are experiencing a lot of crashing then consider taking the time to (1) delete the app (probably best to delete from both the phone and iTunes) and then re-download it to the computer (it will be a free re-download) and install it from there. Also, try not to install too many apps and delete the ones you really don’t use.
If your phone is acting funny, then you can do this to make the bad goblins go away. Hold down the HOME button for about 8 seconds. You won’t get any kind of prompt or signal that anything happened so just count to 8 slowly and then release the button. This should shut down any background processes that are out of control and likely to lead to trouble.
If the phone is really messed up then you need to do a reboot. To do this, hold down the HOME button and also the Power button on the very top of the phone (the one above the ear speaker). Hold them down until you see the Apple logo appear. This will reboot the phone and reset everything.
One last tip (not about troubleshooting): if you want to do a screencapture on your iPhone hold down the HOME button and quickly press and release the Power button. The screen will flash off briefly to let you know that a picture of the screen was captured. It will be stored in the place where your iPhone camera stores pictures.