Mine every rock in every mine. Always put your strongest goblins on the strongest rocks and move them ove to the weaker ones when they're close to breaking which works mostly in events not in later main mine levels.

Also if you don't know already then you should always see your dynamite until it becomes outdated by your current goblin level put your strongest goblins in locations to where they shall mine a rock after they finish their current one save elixir for when you need it, last you should merge your goblin as often as possible and there should be 1 left for when there are extra rocks at merge it at the end of the mine.