Label your floppies!
Don't ever, ever type FORMAT C: at the DOS prompt!!!
Remember to use anti-virus software if you exchange floppies with other users.
One floppy at a time in the floppy drive! Yes, people actually try to put in too many. *g*
Make sure the floppy drive light is off before you press the eject button.
Keep floppies away from magnetic fields or you could lose all the data.
Use ScanDisk or chkdsk on your floppies to check for errors.