When it comes to good-looking abs, getting lean and building muscle are both part of the equation. While most people think that diet alone will get you to a six pack, it's actually a combination of making smart dietary choices AND doing the workouts to match your effort. To have visible abs, you need to have somewhere between 8-12% body fat (this percentage can vary between people).
The first thing we suggest is keeping a diet log for a couple of days. Apps like MyFitnessPal can be very helpful with this. Once you do this, begin making small modifications to your diet, rather than switching to an aggressive diet overnight. If you make too many drastic changes to your diet or lifestyle, it becomes very easy to fall back into old habits quickly.
A good first step is to cut down on so-called empty carbs – examples are as sugary drinks and junk food. You can also try to make subtle switches like brown rice for white, veggies versus starchy vegetables, and reducing portion sizes. A great place to start is by cooking at home versus eating out. When you eat out, you often times end up overeating, or eating less nutritious foods. A good plan is to include lean protein (poultry, fish, eggs, beans, and beef with each meal and to consume high-quality carbs like vegetables and whole grains around your workouts when your body needs energy.
As for the exercise portion, it is important to include strength training exercises such as squats, deadlifts, and presses into your workout program. Cardio is also a great addition to your workouts if you can mix in high-intensity interval and steady state sessions.