Caving

Caving is one of the most important activities in the game. Gems and time crystals can only be found naturally in caves (there is another way to get them without an in-app purchase).

A good general approach to exploring caverns is to follow the right most path. This helps you stay clear on what you've explored and not. It only fails when there's a circular connection and in that case your Light Sources indicate you've looped back so it's no trouble.

Another way to keep track of which tunnels you've explored or stripped of resources place a block of limestone at the entrance(s). It looks different than un-mined limestone so you'll know you placed it as a signal. You could also wall it off with stone because it is abundant.