What to do before formatting my computer?

I'm going to format my PC. I have already have a backup of important files. I use this PC to sync with my iPhone. Now I don't want to lose all the applications and contacts which are present in the iTunes library(Songs don't matter). What do I do? Any other tips before I format my computer?

You say you have backed up your important files, have you backed up the applications and contacts in the iTunes library? Formatting will remove EVERYTHING from the computer. Be absolutely certain that everything is backed up. If you don't know exactly what you are doing, I suggest you get an external drive large enough to store your entire HDD and clone the old drive onto the new, or make an image file, and only then move on to formatting so that you can go back and recover anything you might have missed.