Keep the flame about an inch or two from the bulb. it's really not an exact science, just don't let it get close enough to char the bud. You will usually take multiple hits. Gring your weed; you want as much surface area on the bulb as possible. Candle's are better just so you don't waste lighter fluid. And, finally, the pot will be a full brown color. Don't let it get charred. You can still get some vapor off this brown duff, but you'll most likely burn the plant. Instead, save it for baking. You'll need more duff than fresh bud, but it will fuck you up.