Chris Walton talks about avoiding crashes
NO-COST OPTIONS Run emergency disk. This is a program that comes with the system software on your Mac. If your Mac has floppy disks, you will find it on a disk marked 'utilities'. If your Mac came with a CD-Rom, look for a folder on the CD labelled 'utilities'. This program can detect and repair problems with the directories on your hard disk, and should be booted from the disk or CD and run once a month.
Rebuild the desktop database. This is done by holding down the command and option keys as your Mac is starting up (command is that little key with the Apple on it). TechTool is a freeware program which can be downloaded from the Internet. TechTool can do a better job of rebuilding the desktop. TechTool deletes the desktop database and forces your Mac to rebuild it from scratch.
Zap the Pram. Some inexplicable problems can be caused by corrupted Pram. The Pram is where certain preferences are stored in your Macintosh computer. They are kept in a chip rather than on the hard disk so they will not be affected if you reformat the disk or reinstall the system software. You can use TechTool to zap your Pram, or you can zap it by restarting your computer with the command-option-p-r keys depressed. Release the keys once you hear the second sound of the start-up bong. Please keep in mind that once you have done this, some control panel settings, such as your location, will have to be reset.