Planks are a great exercise to incorporate in your everyday activities.  Not only do planks work your core, but it also activates the quadriceps, glutes, shoulders and triceps muscles.

There are many versions of planks.  Full planks as shown in the above picture, planks resting on elbows, side planks, and reverse planks.  As you perform this exercise, try and hold the position as long as you can with good form.  Have a time set in mind and work towards that goal.  You will sure see improvements as you continue to work and challenge yourself.