I have not used that particular product, but I can pass on some pointers on prep. big things are to follow the manufacturers instructions to the letter.
I mostly have used baked on products, but most are similar in that they use a phenol as a solvent as a suspension agent that evaporates or gets baked out and then allows the remaining parts of the resin to harden. The surface that is going to be coated needs to be free of all grease. Also it is better to have some rough surface for the coating to adhere to. If you are spraying over the existing coating, you may want to rough it up a bit, Most manufacturers recommend sand blasting first. Some will recommend Blasting, and then parkerizing to give an absorbent finish for the coating to adhere to that is bonded to the metal itself. You can spray right over an existing coating, but adhesion over the long term will not be as good as coating a blasted or blasted and parkerized surface.
Back to de-greasing. Before you start, make sure you have some rubber gloves that are already free of all oils. I am cheap and wash my parts in hot soapy water with Dawn detergent. It degreases really well and leaves residue after rinsing with hot water. After washing and rising, ensure that you do not touch any of the parts with bare hands or place the parts on any surface with oils from here until the parts are coated and dry. I also warm parts in the oven to ensure that they are dry and to speed the contact dry time of the coating. I use baling wire to use as handles for the parts and to suspend the parts while spraying and drying. (Ensure the wire has been degreased as well before starting.)
With Duracoat, the next thing you need is patience. Don't touch parts until they are dry, don't assemble them until the manufacturers specified time, and don't shoot until things have set for the full few weeks of cure time. I've seen folks shoot guns that were just a few days after coating with Duracoat, and ruin the work. They will say that Duracoat is junk, when it was really their failure to follow instructions that ruined the coating.I've seen other folks who were patient and waited, and the Duracoat holds up remarkably well.
So, Degrease, and when you think you got rid of all the grease, degrease again. Don't touch parts early. Do't shoot early and if you can get the surfaces prepped properly with sandblasting.