To ensure proper application of any ceramic coating, the surface preparation is the most important factor. The prep process includes a full decontamination of the paint surface, using a Multi-Purpose Cleaner (W5) , Iron Fall Out Remover (W6), Ph neutral shampoo with no additives (G Wash or W4), followed by a clay bar or towel.
I personally like using the chemicals at the same time as the clay so that a physical decontamination and chemical decon can be done in 1 step. After a quick wash to remove any left over chemicals, use a Gtechniq MF4 Diamond Sandwich Microfibre Towel to dry the vehicle extremely well and remove drips from anywhere including mirrors and door jams. At this time you would start your paint correction process, using your favorite combo of polish and compound to bring the paint to a satisfactory level before coating. Once your paint correction is done you would then use your Gtechniq Panel Wipe by spraying onto the MF1 microfiber cloth and wiping each panel down to remove any residues/oils left behind from the paint correction process.
I would recommend going around the car twice with panel wipe to be sure the surface is fully prepped. Once done with the second round of panel wipe you are ready to start your application process.