To begin with slightly tilt your pelvis to allow you to flatten your lower back and zip yourself up, then gently squeeze your bottom muscles and lift your pelvis up off the ground. Biggest thing is to feel like you are maintaining your starting back position and not going up too high. Hold this position for about 5 seconds and slowly lower down and then repeat for about 10 -12 repetitions. The bridge is a nice stabilising exercise for the lower abdominals and butt muscles.

The clam is an exercise that targets a wee muscle in your bottom called the PGM (posterior gluteus medius) which is quite important for pelvic stability particularly when running or climbing out of your seat. I think the important part of this exercise is to remember not to move the hips back when lifting the leg, so keep a hand on your butt and you can feel what you are up to.

Keep the feet together and then take your top knee away from your bottom knee. Do the movement quite slowly and after a few you can start to feel a slight burning feeling in your butt. Try to do 10-15 repetitions both sides of course.

The picture shows the full side bridge but you can modify it and do a half bridge from your knees instead of your feet, with the biggest thing to remember keeping your shoulder, hips, knees or feet in a nice straight line.

Last but not least, the plank. Again I have given the full version of this exercise in the picture, but you can also start with your knees bent on the floor and come up from that position. The biggest mistake that people make with this exercise is that they forget about their neutral spine position and start to sag in the middle causing their lower back to become sore.

 
You really want to feel like you are using your abdominal muscles and see how long you can maintain that position, start with about 10 second holds and build up from there. Try doing five 10 second holds and then increase out to 20 seconds and so on.