Playing a crown can take away one layer if no other target is available (i.e., popping a bubble. Crowns will NOT however remove a rock layer on (some growth mode levels, e.g., 313.)
Therefore it is usually better to play a word (4-letter for example) along MULTIPLE STONES than "around" a single stone. You could remove 1-layer from 4 rocks in one move but not 4-levels from one stone.
It is better to blast multiple stones than one stone multiple times in the same move.
It is better to blast one stone and play adjacent to other stones in the same move.
On some levels, the blasters seem to have little or no effect across "dead space" in the game tableau (222?, 170 maybe at first, but not 175) -- this behavior may be different earlier in a game or perhaps if the stone already has cracks? Some levels seem to make the dead space a barrier while a blaster played "on the active tableau" affects the stones just fine.
Do blasters work better (sometimes?) if CLOSER to the stone than if far away?
Play to hit multiple stones on a single move (blasters or adjacent tiles)
Concentrate on a few stones on subsequent moves
On a crowded board, it is better to destroy a few stone blocks completely (obtaining room to play) than to crack every stone on the board.
Playing multiple adjacent tiles doesn't give better results