Step 3: Iron it on
Once you are done ironing, cut the paper around the board if desired, and drop the paper and board into a container of water to soak the paper. Let this soak for about 10 minutes. With the cheap glossy laser paper from Kinko's the time is much shorter than the high quality inkjet photo paper. Once the paper is soaked, peel the paper off both sides. This should leave the toner and a thin layer of the paper along with the glossy stuff on the copper board. Using your thumbs or an old toothbrush, carefully rub off the extra paper pulp and junk on the board. See pic, below showing a board with half of the pulp rubbed off.
Once the paper pulp is rubbed off, carefully inspect the traces and features on the board for small imperfections and stuff that will cause problems later. Key areas to pay attention to are closely spaced traces and pads where it is easy for paper or glossy coating to bridge and keep the copper from etching. Also, you can achieve very fine pads for doing TSSOP, QFP, and other fine pitch packages using the toner method if you carefully scrape between pads using an Xacto knife or similar prior to etching. During ironing, the toner tends to smear slightly, so very fine pitch pads tend to mush together. Using the knife, you can scrape between the pads or traces to make sure the copper will etch between. If you are careful, there is no reason you can't get 800 micron or even 500 micron pitch pads.