Step 1: Tools of the trade
The purpose of the sponge is as follows; the sponge is porous, so it holds water. Rubbing a hot soldering iron tip on a wet sponge causes the solder to contract at a different rate than the soldering iron, helping to knock off any globs of solder that may be clinging to the tip. NOTE: Make sure the sponge is damp (not soaked) with water.
600 Grit Sandpaper
The second tool of the trade, is 600 grit sandpaper. NOTE: Paper ignites at 451 F, so make sure the iron is unplugged, and has had time to cool before using sandpaper. You will only use sandpaper if the tip has been abused by the previous technician, student, or co-worker.
Tip Tinner / Cleaner
You wont need this if you've got some extra solder. I wouldnt recommend spending the money to buy it unless you have a high-end soldering iron ($XXX.XX price range) for all intensive purposes, regular solder will work just as well for what we're doing.