Hey! This is a good question. I've directed and been in a few shorts - and several theatrical productions... so I'll answer your question from my experience as a performer.
Be prepared. Be prepared. Be prepared.
a) While I assume everyone is a volunteer, treat the shoot as a professional one. Set a good example for everyone on set - and for the future.
b) Go in knowing which shots you want - and the best way to transition your gear between shots. The easiest way to frustrate your cast (thus losing performance value) is to be slow in your transition from different shots. Especially with volunteers, understand and appreciate that they are giving you their time -- make it as painless as possible. An example of this... If you and your crew are loading in on location at 6am, don't have your cast show up at 6am. If their call time is 7am, be ready to get them into costume\makeup AT 7am. Performance energy slumps and attitudes get grumpy during long pauses in action.
c) While problems inevitably arise, have plans for everything. Know where your power sources are... How much extension cable to bring.. etc... Scout the location to see where the available light is. Do the sun or shadows move as time goes on? What time does the sun make your set look great? Are you batteries charged? etc..
d) Don't be too proud to listen to ideas from your cast. This makes them feel included and helps them take personal responsibility of your project. You don't have to implement their ideas, necessarily... but your willingness to be a creative collaborator will help you in the future - so start the habit now.
e) Be polite when giving your cast performance notes. Yelling and screaming raises tension in everyone on the set - reducing the actor's ability to show you any desired emotion through your lens. If a particular actor doesn't 'get' it... Try using different words. Instead of telling him to be 'sad'... Ask him if he has a dog - then imagine if the dog got caught under the bed when his house was on fire. Sometimes, little imagery exercises like that will spark that fire you need. But most importantly - out of all of this - treat people with respect - or the problems on set will come through on film - and chances are, no one will want to work with you again.
Now, this certainly does not give the actors free reign to be divas.
Everyone needs to understand that each person is on the same team - working toward the same goal.
In short - to make everyone feel comfortable on set - do your job, and do it well. Have a crew whom you trust... and they will trust you.
I know this seems like a lot - but it boils down to being ready, being smart, and treating people with respect. Keep these things in mind, and you'll have a great shoot.
Best of luck!
