Your board should be stored in a cool dry place, out of direct sunlight and either rolled up and stored in the bag, If storing for a long time without use, make sure you ease the tightness of the roll so that there isn't lots of pressure going through the strap into the board, especially near the fin box if you have one of these. It may also be an idea to store the pump separately if you do have the space for this. 
 
If you are hoping to keep your board inflated, we recommend keeping this on a flat surface or upright (not kept on a rack for a long duration) to prevent changes to the shape of the board.  If you are not going to use it for a while you should reduce the pressure to below 15psi and keep your board in the cool and dry.

Before you pack your board away though, it is very important that you rinse everything in fresh water (Board/Bag/Paddle/Pump/Leash etc) and allow to dry completely before packing it away.