This is a great pose to help loosen up the lower back as it is quite a shallow bend.

Lay on your front face down.
Bring you arms beside you with elbows close to the body.
Make sure the forearms are in a straight line.
Finger tips should be about level with your eyes.
As you breath in lift the upper body.
Your push should not come from pushing down on the arms it should come from your back muscles lifting.
The arms are there to support not carry all the weight.
Relax the shoulders keep them away from the ears and lift the front of the chest forward.
Your gaze should be ahead this will depend on what is comfortable for your neck.