Burning it sucks for many reasons like, makes your meth taste like shit each hit, reduces the potency of the whole bowl you got in there (less potency equals a lesser quality high) and it makes your pipe dirty which in the future each new bowl you pack is finished quicker so you're essentially wasting your shit. My tips are
1 don't let flame touch the glass at all
2 make sure you're twirling enough so the puddle is not getting to much heat on one spot
3 it should stay a yellowish color until its all gone, if it goes brown you burnt it
