If you purchase your tickets online through Universal's website, when checking out with base tickets, it offers you the choice to upgrade your base tickets to park to park tickets for just $10 instead of the normal $20 it costs to have that option on your tickets. You also save $20 per person off the GATE price. Don't wait until you get there to buy your tickets. And seeing how BUSY/CRAZY/CROWDED it will be, you can pre-purchase the Express pass add on while buying your tickets too, if you planned on buying that.
Buy them online and choose the option to either print them out at home (I didn't do that) or you can have them mailed to you (I did that one)