Make sure you get a recipt from the parking person and bring it with you. Then remember when you are buying it to turn it in, they will take the $11 off the price. I usually forget one of the above steps and have to retrace my steps. You can do it when you buy it, or at the AP processing center, though only on the day you bought the parking on the pass.
Also it doesn't matter who has parking on their pass. I have suggested to friends with kids where the parents may take the kids seperately, to put the parking on the kids pass. If the kids is the one who will usually be going put the parking on their pass. My daughter likes to hand them her pass as we enter. The last time, the guy commented, well you have parking but don't have a car. I think he though I bought her the premium pass and me the cheaper pass. However we both have the premiums, I just pull forward and let her "pay". My mom loves the fact that my daughter has parking. If we go with my parents, they make sure that she is in their car so they don't have to pay.