I get baffled when I see, even now, fellow writers *still* losing work when it could be avoided. Sure, sometimes despite your best efforts, the technology will fail and take something from you. But you can try to limit the damage. So here's what I do. Obviously you all have your own methods, technology, your mileage may vary, etc etc. But this works for me. This is my
1: Create a new file, and SAVE IT IMMEDIATELY. Don't create a new file, start working for several hours, and then go "ah, better save my work so far". The computer or the software will know that you haven't saved, and will crash or explode. But if you have already named and saved it, you can just keep hitting Apple-S or Ctrl-S every few minutes as you go. My hand is trained to do so. I don't even realise I'm doing it anymore. I get palpitations when I see someone working on a large file called "Document 7" or whatever, indicating they haven't actually saved it yet. Save the file, save the world.
2: At the end of the work day, save the file one last time. If you're using screenwriting software, save it as a rich text file (.RTF) and as a PDF too, just in case the software stops working or the original file format gets corrupted. Sometimes I'll do this halfway through the day as well, if it's something I really, really, really don't want to lose.
3: Email the files you saved to a special Gmail account you have created just for backup. You get over 7GB of storage, which you'll probably never fill with documents. In the subject line, put the title, filename, draft number, and what page you are on. This will help you know what stage you were at, in the event you need to go looking for a copy. I usually put the draft number in the filename too.
4: The next day, copy the file (so you have a "Filename_copy" backup right there in the folder), start working, and repeat steps 2 and 3. Every day, you have a copy of the day's work sent to your Gmail backup, so you will have copies of *everything*.
5: Once a month, copy your entire user folder or documents folder to a portable hard drive. Do not use this drive for anything else.
6: Once every 6 months, copy your files to a different hard drive. Try to keep both drives in another location, or even in different parts of the house.
That's it. If your 6 monthly backup drive dies, you have your monthly backup drive. If that drive dies, you have a copy of every single day's work, and every single draft, in your backup Gmail account. The constant Apple-S or Ctrl-S and emailing the file to yourself means that if there's a crash, you should only ever lose a few minutes' work. Gmail is free, hard drives are fairly cheap. There's no reason to be careless. Update: I also use Dropbox as an extra layer of safety, and for accessing files on the move - it's free, has 2GB of storage, and when you copy a file into the special folder, it automatically syncs across any devices/browsers/computers you want to access it from. Very useful. That's not my referral link by the way, because it'd make it look like I was only mentioning it to get free extra space.
Obviously this won't help you if you accidentally delete or overwrite the file at the end of the day just before emailing it to yourself. So try not to do that. But even if you're taking a break for lunch, email a copy of the file to yourself, just in case. Or even any time you get a few pages done. Only takes a minute to email a copy to your backup Gmail account. Just get a copy of it somewhere away from your main computer, as soon as possible.
Yes, it's a little bit over cautious and obsessive, I admit. But hey, I'm a writer. Paranoia and constant fear go with the territory. Now go and back up your files! Quickly! Before something goes wrong!