How to get a six pack

We all know that getting perfectly defined abs is a lot harder than defining your arms & chest. This is because you can hold more fat in those other areas & still have definition. Whereas you will need under 10% body fat to show off any sign of your abs. 
Where to start....
It takes a lot of work in both your diet & exercise habits, but it can be done!
Just remember that it starts in the kitchen.
You will need to review your calorie intake and establish how many calories you eat & burn each day (Try MyFitnessPal). Once you know this you can get yourself in a calorie deficit and start forcing your body to start using fat stores for energy. You can create a calorie deficit by either eating less, exercising more or combining both. 
Foods to Eat
In addition to a calorie deficit you should look at the foods that make up your diet.
Avoid foods that contain a lot of sugar such as chocolate, fruit juice, sweets & refined carbohydrates such as white flour- bread/pasta, white rice.
Instead, eat 100% whole wheat grains, whole wheat bread/pasta, brown rice, beans, & vegetables, lean proteins (Chicken, Turkey, Seafood) & unsaturated fats such as olive oils, avocados, nuts & seeds. 
Alongside having your nutrition on point, exercise plays an important role in defining those abs. Your workout routine should include 3-5 sessions of cardio per week lasting 30-60 minutes. Such as running, biking, swimming, circuit training etc. This will help you burn extra fat. Then add in some ab exercises to your routine. Three examples to get you started are below:

The Plank

Start on all fours like you would in a press up and then lower your forearms to the ground, keeping your elbows under shoulders, and extending legs out behind body. You will be in a straight line from head to heels.
Give it a go and see how long you can last. 

Mountain Climbers

Start in a high press up position with your arms straight and your body in a straight line from your head to heels. Bring your right knee in and back out and then repeat with the left side.Try as many as possible in 30 seconds. Repeat 3 times.

Russian Twists

Sit on the floor (balancing on your tailbone) and have your legs bent and elevated so shins are parallel to floor, with ankles crossed. Have your hands clasped at chest and torso leaned back and rotated to left side. Squeeze your abs muscles and rotate your upper body to the right side. Reverse movement to return to start. That's one rep. Try 4 sets of 12 reps.