Develop some killer abdominals
You probably know already that to see your abs, you need to have a low level of bodyfat. No matter how well developed your abdominal muscles are, you won't see anything if there's a layer of fat covering them up.
But dropping fat is only half the story. If you want a decent six pack, you also need to build rectus abdominis.
The six pack look is the result of bands of connective tissue that "cut" into rectus abdominis. The more developed the rectus abdominis muscle, the deeper the grooves.
There are some people who are genetically gifted in the abs department and don't need to do a lot of direct abdominal work. Unless you're one of them, you'll need to train rectus abdominis if you want a six-pack that looks good on the beach.
Ball Rollouts 2 sets x 5-10 repetitions (60-90 seconds rest between sets)
If you've never done rollouts before, start off with a basic plank. Then move to rollouts with your knees on the floor before trying them with your legs straight. You can also use a loaded barbell or an ab wheel, which is one of the few abdominal exercise devices worth using.
Rope Crunches 3 sets x 8-12 repetitions (60-90 seconds rest between sets)
Kneel in front of the rope, hold the rope with both hands with your chest upright. Begin by flexing at the hips, bringing your torso down to towards your legs as you pull the cable down, hold the position as you reach the bottom, then slowly return to the starting position.
Pallof Press 2 sets x 5 repetitions per side (hold each rep for 5-10 seconds)
The Pallof Press is named after physical therapist John Pallof. It might not look like an ab exercise, but once you've tried it you'll feel it straight away!
Start with your feet roughly shoulder width apart and knees slightly bent. Press the cable out until your arms are fully extended in front of you.
When you press the cable forward, the forces trying to turn your torso to the left or right are increased. With all the resistance coming from one side, your "core" muscles have to work hard to prevent your body twisting.
From there, you’ll want to "brace" the abdominals as hard as you can. This involves tightening the abdominal muscles as if you're about to take a punch in the gut.
Bracing your abs during the exercise is really important, as this has been shown to increase muscle activation, making your abs work harder and giving you good results.
Aim for a total of 3-5 repetitions per set, holding for around 5 seconds each time. Be sure to do an equal amount of work for both sides of the body.