Suit the location to the play. 
Last year we did Hamlet in Lone Fir Cemetery, and the year before that we did The Tempest (literally) in a fountain. 
—Michael Godsey, Portland Actors Ensemble 

Bring a backup light source.
We were doing Midsummer, and the generator failed and the entire show was plunged into darkness right at the beginning of Pyramus and Thisbe. We finished by the light of cell phones, bike lights, and one rather bright light-up Frisbee.
—Brian Allard, Original Practice Shakespeare Festival 

Expect the unexpected.
A train, a helicopter, a police car or fire engine with sirens blazing, a drunk guy on a skateboard with a boom box, a family of raccoons, a cat in heat, Guatemalan Independence Day celebrations, a terrified deer prancing across the stage, hailstones the size of golf balls, and actors passing out from heatstroke are ALL possible—and have happened during B&B outdoor shows.
—Scott Palmer, Bag & Baggage Productions 

Avoid any set piece that can act as a sail.
Last year at a Much Ado About Nothing performance at Stoller Vineyards, we had the stage manager, the crew, the artistic director, and several members of the board of directors and cast members hanging on to our set for dear life in the middle of a windstorm. 
—Daniel Somerfield, Willamette Shakespeare

Attention, sneaky sippers: bring plastic, not glass. 
Pour your alcohol into nonglass containers (think Big Gulp or Starbucks cups). If you drop a bottle of red wine and it shatters, Lady Macbeth will obsessively begin to clean up the spill. 
—Scott Palmer