WANT STRONG NOTICEABLE ABS FOR THE SUMMMER?? Here are some tips::

It is important to perform exercises that involve the core for at least 5-6 times a week. Do no more than 3x a week of Ab isolation exercises that work the ab muscles in only one plane. There is no such thing as upper or lower Abs, rectus abdominis makes up the whole ab muscle in the front, plus you have your muscles on the side which are the internal/external obliques and transverse abdominis, which is layered deep below the internal oblique. So it is important to work your abs through all the different types of planes.
Most compound exercises, especially ones on the Swiss and bosu involve the entire core. For example a standing shoulder press on the bosu ball is a great Ab exercise when (form is correct and Abs are tight through out the whole set) as well as a shoulder exercise. So stick to mainly standing exercises, and if you do sit or lie down, try to do these exercises on a bosu or swiss ball.
Erector spinae and pelvic exercises are a must if you want a strong core and good posture. These muscle must be strong stabilizer muscles so the Abs can be worked correctly. If your lower back is weak than it will get worked more than your abs will during a sit-up.
Lastly, Weightlifting- cardio - healthy eating, is the only way to a noticeable strong fit midsection. Weight lifting builds the muscular Ab look but fat loss through cardio and healthy nutrition is the only you can show those muscular Abs off.