Remember how to do breath-of-fire? Good!
Lying on your back, press your low back flat, into the floor, and lift your head and shoulders off the ground. Have your arms parallel to your legs, and the floor. Now lift your feet up so your toes are at eye level. Gaze out beyond your toes and begin breath of fire. Be sure to keep the low back pressed flat!
Do it for 10 seconds to start. When that becomes easy, increase up to 30 seconds. Then work up to 3 minutes!
When you are ready to stop take in a deep breath and perfect the posture for a few seconds then lay back down flat and relax. Let the energy flow for a minute or so.
If you need to get going right away then don't lie flat but pull your knees in, place your hands behind your knees, and roll forward to sit up.
The modified (easier) version of the pose is here
You might enjoy this
as a preparation exercise, to do before and after. It will help you develop better awareness of the muscles involved, hence better control.