Roughening the surface removes the layer of oxidized rubber and parting compound from the surface to allow a chemical bond to the patch, so don't under-do it. I use acetone at home and an alcohol wipe on the road to be sure any oils or waxes are removed. Roughen/clean an area larger than the patch and apply plenty of vulcanizing fluid to the entire area. Let the vulcanizing fluid (not really a glue) dry naturally, don't blow on it. Don't touch the tube or patch bonding areas with your fingers. Use the narrow edge of a coin, wrench or tire lever to "stitch" the patch down, especially the edges, for good adhesion; pressing with your fingers is not enough pressure to ensure a solid void-free bond.