Always check your settings before you start shooting, especially if you are taking important shots.
(I can't admit to how many times I'd set the camera to 6mp JPG because I was posting some photos for a for sale ad or some other process and then forgot to switch back to raw, or forgot to check what mode I was in, or had switched to one type of ambient lighting and then shot another etc etc etc.)
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edit: After finally reading the earlier advice, I noticed
PancakeFlipper said the same thing on the first page - so credit where credit is due.
The other thing I'll add is 'pray and spray' works - when shooting moving objects or hand held macro or where your depth of field is really small, burst mode can be a shot saver - you'll have to throw out 90% of the shots, but you'll have a better chance sometimes of getting the 10% you really wanted.