I assume you're talking wing shooting clays vice a trade gun type trail walk.
The ones I've been to have been based on a 5-stand type setup. Lets people stay in the same location so they can set up a small loading table to keep their supplies on. The score keeper(s)/trappers have to stay on their toes to make sure they've got the right shooter and target presentation as there is a lot of coming and going as people shoot and reload.
Usually 15-25 targets thrown with a limit on the number of hammer falls allowed before calling a miss. If you don't place a limit you will have folks taking all day and burning thru a lot of targets due to misfires (lets face it, we've all been out there with "that guy".)
Targets should be a good mix of presentations. Easy incomers and out goers, harder crossing shots, springing teal, etc.. Obviously the location and trap availability will play a big roll in that. You do need to be able to separate out the really good shooters, either with some difficult shots on the course of fire or with a shoot off later. No doubles presentations as some people like to use their trade guns for this.