the trick is to maintain a certain level of heat consistently as to not burn it
hold the lighter about 1 full inch away, as soon as it starts to melt you roll the bowl back and forth, moving the now liquid meth back and forth, rolling it like putting a baby to sleep. This way the tiny meth puddle doesn't sit in one really hot spot and burn.
If it tastes like shit, it's burnt. If it's brown, it's burnt (or is heavily cut, or both). If it burns your mouth, it's burnt.
You'll quickly get the hang of it after a few tries. It's really not that complex or difficult.
Remember, you're not trying to smoke meth, you're trying to get it just hot enough to VAPORIZE, but not hot enough to COMBUST. Imagine it like getting water to STEAM but not hot enough to BOIL.