For the push ups, start in the low position and push up with slow steady motion until the top of the movement and then slowly lower back down under control. Breathe in as you go down and in as you push back up. This is one rep.
Free standing squats, fold your arms across your chest and perform deep knee bends slowly, under full control. At the bottom of the movement push with your thighs and come back to the top position. Breathe in as you go down and out as you come up.
Crunches, start by lying on your back on the floor with your feet on a bench or chair. Hold your hands beside your head (NOT BEHIND). Raise your upper body from the floor as high as you can. Breathe out as you raise and in as you lower your upper body. Do not hold you hands behind your head and pull as this will put excessive strain on your neck.