wear a hat
it's a good idea to carry your own glass/mug/shotglass or other recepticle for drinks while wandering about the playa - it's polite and you look all prepared and cool
it's a good idea, particularly if you're a woman, to wander with a group (particularly if you'll be partaking of any sort of inebriant) - you're safer on the playa than in most places on earth, but as the population increases, the number of bastards increases too - looks like we're going to hit 35,000 people this year. Thats bigger than San Luis Obispo, where i'm from.
if you go it alone, just drink anything offered to you from your own glass (that way you get to watch them pour it). Remember that doing toasts is both fun and a good way to see if they're willing to drink whatever they're serving you - if they don't, maybe you oughta ask for a nice cold beer, one that you can open yourself.
I'm not trying to make you paranoid, just call it a friendly word of advice.
Remember that, generally speaking, seven of ten people you meet on the playa will treat you like a long lost and dearly missed old friend, and when you meet and hang out with them you will make memories and friends that may just last a lifetime. One out of ten people will be suffering from the heat, or a hangover or a bad moment in their relationship or one of "those" days. One will be busy doing something or be the girlfriend, sister, child etc of a burner and really have no clue about how to act with strangers at burningman (you never know how that will turn out). That last one, they may fall into that unpleasant category, they're the ones that put stupid things in the porta potties, steal parts of the art installations, leave bags of trash lying around, slip people drugs as a joke or for some less savory purpose, and they just might steal your bike. They may fall into one of the other categories most days, but it might be just your luck to run into them on "that" day.
So stay aware.
It's just another part of the radical self reliance thing.
And don't be afraid to ask for help, or yell for help if necessary. There are seven burners who will come and help you.
Seriously, we won't mind.