I do a lot of work as a volunteer Mac Technician with a local non-profit organization. Some of that involves taking laptops apart to refurbish them and then putting them back together correctly.
I replaced a hard drive in a iBook G4 today and it was the first opportunity that I had to use the magnetic pad from iFixit. I was able to lay out all the screws in the order they were removed without getting any mix-up. The re-assembly went smoothly as I was able to pick out the correct screw at the necessary time and had no "extra" screws left over at the end.
Get a magnetic iFixit pad and use it. It also helps to have the iFixit step-by-step guide on screen to be sure that you are doing the right thing at the right time.