Some very effective beginner abs exercises are:

Bicycle Exercise:

According to a recent study, Bicycle exercise is best for developing and maintaining six packs and to reduce the waist line. For doing Bicycle exercise we should lie on the floor and lace our fingers behind our head and then bring your knees inwards towards the chest area and then lift your shoulder blades off the floor. This, you have to do without pulling the neck. Then, straighten your left leg out and at the same time turn the upper body to the right along with that take your left elbow towards your right knee. Next, you need to switch sides for that bring your right elbow towards your left knee. This, you can repeat by alternating the sides in a pedaling motion for about 12 to15 times.

Sit-Ups:

Take a mat and lie down on your back, bend the knees, make sure to place the lower back flat to the ground with both hands reaching up and keeping our eyes locked to any one object on the ceiling. Breathe out the air as we contract. We should do it slowly and carefully until we feel that we cannot handle anymore. We should never let the abs loose during the workout.

Crunch:

It is similar to sit-ups; instead of trying to get the upper body up we need to curl our chest towards the hips. We should do maximum contraction by emptying air.

Reverse crunch:

To do this, we need to lay on your back, place the lower back flat on the ground with both hands on the ground for balance and support. Slightly bend the knees and pull both legs up towards hips (Like L shape). Flatten the Abs and slowly curl the hips towards the chest and hold it for few seconds and then gently release down.

Most importantly, get creative with your ab workouts.  Use a swiss ball, medicine balls, kettle bells, and other weights and equipment.