An excellent exercise to work the abdominal muscles is called Toe Touchers. You do not need any equipment to do this exercise (though you can add weights eventually) and it utilizes your own body weight.

Movement:
Lie on your back, on the floor and elevate your legs up into the air. Make sure you keep your lower back pressed flat into the ground and do not arch. Pull in your abdominals.  Exhale and crunch forward reaching your hands upward to touch your toes. (Touching any part of your foot or shins will work!) Please remember, don't pull your chin down towards your chest. Keep your head in a neutral position.

Many people tend to overdo it when starting a back strengthening program, resulting in back strain and pain. Back pain caused by doing too much to quickly can be discouraging. It is important to start of right and work up to more difficult exercises gradually. Strengthening the back should not be rushed.
Before doing back exercises, or any other, it is important to warm up the body. You can do this by walking on the treadmill, doing the elliptical, jumping rope or even running on the spot. This will get the blood flowing and the muscles warmed up and ready for the workout.

When doing any and all back exercises, remember to always activate the abdominal muscles first. Do this by couching or blowing out all the air from your body (pull in and tighten your abs). Maintain this throughout your exercises but remember, do not hold your breath.

The first exercise I will cover in this post will be the PLANK. (Check back for more back healthy exercises that you can add to your program)
 
The Plank: Strengthening exercise for back, abs and neck (also strengthens arms and legs)

Lay on stomach, place elbows and forearms on floor. In a push-up position, balance on your toes and elbows. Keep your back straight and legs straight. (Like a plank) Tighten abs. Hold position for 10 seconds. Relax. Repeat five to ten times. If this exercise is too difficult, use balance on your knees instead of your toes. Do this exercise regularly. Gradually work your way up from 10 seconds to 20, 30, 40 and so on. If you started from your knees, work your way up to doing the plank from your toes.

One of the easiest ways to work the leg muscles is by doing squats. Squats are excellent if you goal is to lose weight and tighten your thigh muscles. However, you must remember the important rules of squatting.

 

 

For proper execution of a squat, stand with your feet about shoulder-width apart and with your toes pointing slightly outward or in a natural anatomical position. Squat down, bending the knees and pushing the bum back as if preparing to sit in a chair. Your thighs should be parallel to the floor and your knees should be in line with your toes ensuring that all the weight is through your heels and not your toes. Keeping your head up, abs tight and lower back slightly arched, drive the weight up with your legs until you are in a standing position. Remember to keep you knees soft and not locked at the top. Once you are standing straight up, squat back down over the same path. 

 

You should feel your Quadriceps (thigh muscles) working the most with the Hamstrings and Calves mildly working during this exercise.  You can also work your glutes as you squeeze them whilst in the standing position. You should be able to complete fifteen to twenty reps without weights in hand.  As you progress you can add dumbbells in hand to make this exercise more challenging.

 

Tips: Always maintain proper form throughout this exercise by keeping your head up, abs tight and lower back arched. Squats are a big power movement and you must execute them with full concentration in order to prevent injuries. Do not use jerky motions or body momentum.