Toner transfer is my favorite method for rapid PCB prototyping down to 10 mil traces. The basic steps are already described thoroughly, you can find some good tutorials on the net :
Step 2 may be very frustrating using an iron. I’ve tried it many times but even with clever tricks like toner transfer with dowel , my success rate is rather low. With a laminator, results are much much more reproducible but you have to laminate the PCB several times to fuse the toner solidly on the copper, « several » meaning « until you’re sick and tired » (15 to 20 passes).