Accelerate until your your dwarf's mine cart has a white glow leaves a trail. While in this state, the following things will happen.

Enemies are automatically defeated when you crash into them.
Spike bumps are destroyed.
Chests are automatically opened without jumping on them.

To maintain your speed, jump over small bumps, avoid going uphill, and stay on downhill slopes as long as possible. You can also bounce off of chests and enemies to maintain your speed.