When you go to immigration, there is a small separate office to the right in front of the big Immigration building. In there they have all the forms, will make copies of your passport pages, take picture, help you fill out form if needed, supply glue to paste picture on form. They're awesome in there. 20 baht for copies, 80 for picture (i think).
Then you just go into Immigration building and get in line. Have your form, passport, and 1900 ready to hand to the officer.