I echo everything Phil said, Susan.
Plus, make sure they specify what the PA system is. I usually travel with a very good system myself. I was once assured by a community event organizer that they had a great sound system which turned out to be a boombox with a mic. Thank God I had mine in the car.
Specify indoors or outdoors. (insect repellent in summer).

If outdoors and it's an evening gig, is there adequate lighting to see the performer?
I've ended up doing a few jobs in the dark, so now I carry a small lighting rig just in case.

Are there plenty of electrical outlets for the amps, lights, etc?
If it rains can the event be moved indoors quickly?

Lodging or a motel for the performer.

Include pretty detailed directions with the contract.

Is it OK to sell CDs? Does the venue take a percentage of CD sales?
We like to know this ahead of time, and not be surprised when the organizer comes up for their cut at the end of the gig.

I'll probably think of more later.

Seamus