don't spit, the enzymes in saliva break down the oils and waxes that are in the polish and mean that its doing nothing for the leather, same as if you use a lighter to heat the polish your best bet get your self some svelte polishing cloths brush polish first then go over with the svelte cloth and some normal tap water until mirror shiny, job done.
Im down at raleigh now. You dont really get taught by the instructors how to polish your boots and shoes. The more senior recruits further through training give u advice on everything u need to know in your first couple of weeks. No spit or burning needed! Selvyt cloth which u can buy here at the naafi then polish and water and perseverance is all u need.