Below is a list of the various boosts you can get in the game that will increase the speed your mines work.
2x Idle Cash Forever:
This boost will get you double Idle Cash forever in all mines.
2x Income Forever:
This boost will get double normal Cash forever in all mines.
Income Boosts:
The boosts from the Shop give you 2x or 10x boosts on Cash and Idle Cash in all mines on all continents. You can also win other boosts like 20x from Expeditions, Daily Rewards and Event Mines. Each Income Boost you use is added to your currently active boosts.
Advertisement Boost:
Watching adverts via the button at the bottom of the screen will increase your Cash and Idle Cash in your current mine for a short period of time. This boost is added to your currently active boosts.
Instant Cash:
When you use an Instant Cash item, you instantly get the Idle Cash from all of your mines on one continent (including all boosts except the permanent 2x Idle Cash).