Lie on your back with your knees bent up so that your feet are as close as they can comfortably be to your bottom. Your feet should be hip distance apart so your thighs are parallel. To stiffen your core do a quick small breath out to tighten and stiffen the external oblique muscles and deep abdominal muscles. Push your heels down into floor to take the weight out of the pelvis and then as your pelvis rises off the ground, gently clench your buttocks so you are doing hip extension not back extension. Don't 'tilt' your pelvis backwards (posterior pelvic tilt) or 'imprint your back ' onto the floor - keep the spine in a natural neutral lordotic curve through the whole movement. Also, don't arch your lower back as you get to the top of your lift. Pause at the top keeping your glutes squeezed on, breath in and then breath out and then start to lower yourself back down making sure you pelvis meets thr ground first not your lower back. Repeat 3 sets of 10 reps.

Use a theraband around the knees to advance to level 3 encourage deep glute activation.
Try with one leg off the ground for a single leg bridge for level 4 - it is important that your pelvis stays level when you do this.