We pretty much have the obvious things like always passing left except in cars, and cornering bowls.

Uh, usually, whoever's weed it is get to choose who hits it first.
When that's at my house, and it's my weed, I tend to let guests who haven't been over for a smoke in a while hit first.

Oh! And newcomers always get first hit of the first bowl. Especially if they've never smoked before.