I have observed that Dolores Park is segmented into several distinct and (sub) culturally consistent sections.

A. Hipster Hill
The Northeast corner of the Park (Dolores and 17th) is the realm of the Hipster. I suspect this is because while they can manage the walk from Valencia to Dolores they are too hung-over to make it up the hill.
Do bring: Bike, Enormous Sunglasses, Skinny jeans that show your butt crack when you sit down, Wear black and more black something army-looking works too, Ipods, beer and small speakers are encouraged.
Tips: Sit directly on grass look bored.

B. Jock Corner
Weekend warriors, dodge ball players, soccer fans, etc…
Do bring: Spandex, knee pads and some sort of ball to chase around.
Tips: be excessively perky and organized.

C. Latin American Club
The locals. Watching the scene and laughing.
Do Bring: Beer, your homies, a dog

D. Scary bathrooms
I have only had the pleasure once, but I heard nothing good happens in this place.
Do bring: protection, toilet paper, a sense of balance and humor

E. Gay cruising + Sunbathing section
Bring: a towel, a conversation starting small dog
leave at home: your boyfriend or life partner

F. Kids and picnickers
bring: diapers

G. Geek Section
This seems to be the spot wear the digirati hangs out
Bring: Food to share and your best portable devices

H. Hipster overflow and family outing section

I. Scary drunks and Hobo section
Bring: Bags full of bottles for recycling, Old English or Night Train.

This is an oldie but a goodie from a now moth-balled blog I used to keep.