Working out your back is a bit harder, but also necessary. The first basic exercise you can do requires you to lie on your stomach. Lift your left arm and right leg about a foot. Hold them in the air for 10 seconds and then lower them. You should then alternate between your legs and arms until you have done a full set of reps.
Also consider using resistance bands to get a good workout of your back muscles. Standing with your feet shoulder-width apart, you should hold the resistance bands and pull inward. Bring your arms in as far as you can, hold briefly, and then slowly return your arms to the starting position. You can try this exercise with several variations. Move the resistance bands or make them tighter to make the workout harder. Start with your foot on one end of the band and pull the band toward you to work different muscles in your back.
Any of these basic exercises will get you started on the way to better oblique and back muscles. Try some variation with them to make sure your workout does not stagnate. Then simply create a routine that you complete a few times a week to strengthen these important muscles.
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