First board: Ignore the Diggy blocks. Just dig to the exit as soon as possible.
Second board: This is the most complex board. If you have some combos at the top row, match them; it'll help a lot. Collecting "happy" Diggy blocks is a must - each one needs only one hit, and gives 3,000 points. Make sure to look for any opportunity to break the stone on the exit tile. The gold striped blocks in the bottom corners will score additional 2,000 points each.
Third board: It's a Treasure Room. Don't rush here - you'll need every point you can get before. With three colors, the Treasure Room will give only few points per move, so you should have at least ten moves left.