Don't: rely on your car stereo to blast music all day
Your car will die if you run it all day, and having to ask for a jump after aggressively pumping EDM to the dismay of your neighbors is no fun. Bring a fully charged portable stereo that you can move around if you get the stink eye. Great dance moves also prove to be a good shield against the haters.
Do: spark up conversation with fellow parking lot people
People who spend a good chunk of their time in the beach parking lot tend to be interesting characters. They usually have good stories to tell and can be a wealth of knowledge. If you're trying to figure out when the best time to go surfing is or looking to score a certain something, your parking lot comrades should be more than likely able to help.