Solving subfloor squeaks
When you remove your carpet you should be able to see little impressions where the floor has been nailed or screwed into the joists. It should be a simple matter to line up your screws and put them in. If you somehow miss the joists you can merrily move a little bit to the side and try again. You might also consider pulling any nails at the squeaky spot as the problem may be a loose nail. Sometimes the squeak is an underlying problem (no pun intended). If the screws don't do the trick you could have someone move around on the floor while you go downstairs and try to locate the problem.