Save often, save habitually.
Save because it will keep you from tearing your hair out when you lose power. I've heard people say they only save when they close the document. I can't imagine such a world.
Ctrl-s is usually the hotkey for save; learn to hit it every 20-30 seconds. If saved, work can almost always be recovered. Even in the event of catastrophic failure, data might be saved off damaged harddrives or storage locations. Data lost in a computer crash is probably gone forever (unless your auto save is very good.)
What a boring post title.
Seriously though, back up your writing. I don't think I can say that enough. Losing writing is losing time. We double check to be sure we punch in at "normal" job. People keep printed sheets of their hours. Maybe they physically sign in and out too. Why would a person be any less diligent in backing up their art?
Beyond saving, how do you back up your writing? Online services (or mozy or whatever,) are literally throwing themselves at people to back up data. At the very least, get some flash drives and get a synching program (yeah, it's MS, but it'll be there in years, right?)
Here's what I do. I edit the files on my flash drive and use this free program (same as above) to copy the files onto my harddrive any time I unplug the thing. If I lose the flash drive, I still have the data. If I royally foul things up while writing, I have a close recent version on my harddrive. I recommend keeping several other flash drives as additional backups, and updating them every week at the least.
Also, email your files to yourself and occasionally burn them onto CD. Anything else a person can suggest on how back up his or her files would be welcome.
Well, the real value in most writing is the practice, but some people do plan (or hope) to get something for it, even if the pay day is many years in the future. Keep everything. Back it up ninety times. Get to know the dates on your files. Rememeber which is newest and which can be replaced. If that data is lost, you will never get paid. Maybe it isn't worth a lot, but few people hop onto the writing scene making millions. Write, then backup, then maybe get someone to publish it, (or do it yourself, though that's a whole different topic,) then get paid.