Dogging Etiquette?

Having always wanted to try dogging and almost managed to achieve it once I find my self really confused as regards what the etiquette really is and even where to start.  The one time I did find a site and even witnessed a car with its interior lights on revealing lots of fun inside, I found myself glued to my car seat not really knowing if I should approach, how I should approach or even if I should look away.  If you are any wiser in this than me, please share your tips with me and help me make the next move