Cave-In Warning
When you see the cave-in warning appear, it is to indicate that spikes are about to impale you from above.
Drilling Card
The Drilling cards are always worth selecting as they speed up your drilling speed which allows you to dig faster.
Shield Card
The Shield cards are essentially second chances and can be used to save a run which makes them a great card to have if you are really deep.
Enemy Card
The Enemy card can be very useful when used as they make it easier to avoid conflict by hindering the enemy so they slow down.
Bombs
Make sure you have a path clear away from the blast before you commit to settng off any of the stray bombs that you find laying around. Anyhting caught in the blast will give you additional gems.
Digibots
When you reach certain distances in the mines you will unlock a DigiBot which you should then make spending coins into upgrading it your priority. Your DigBots will dig for gems when you are not actively playing the game which makes them well worth investing in.
Free Gift Box
Make sure you take advantage of the free gift box when it becomes available every 30 minutes as these will contain a random assortment of Ability Cards.
Freebies
After you have spent most of your coins at the start of the game on Digbot Upgradaes you will not have a lot of coins spare to spend on actual cards so it is important that you take advantage of the freebies like the gift boxes whenever any become available.
Time Cheat
Set the time ahead on your device if you want do not want to wait for your free gift or if you want to collect the gems form your DigiBot immediately. Remember though that once you set the time back to normal the cooldown time that you removed from everything will be added back on.