Belly Bounce

If you dive to your belly, pressing a direction on the joystick and the crouch button, you can jump up as quick as you go down. Hit the crouch at the instant you belly flop in the dirt, hit a direction at the same time and jump up in that direction.

It's definitely better for dodging than jumping, especially if the ground is uneven or grassy. You also have the choice of staying down if the cover is good, get a bit to eat, switch clips, whatever.