What is the best way to start a fire instantly?

I tried a few different ideas and they all worked up to a point. The lot I'm trying to burn down is too large and it would take forever to decorate it for maximum flammability or I would need an army of spellcasters to burn it down. It would easier and more effective on a small crowded lot. I may postpone this storyline while I put together a lot in my spare time that I can burn down.