Program them for yourself and test them. This is the best way to get a feel for how movements impact each other, how long they are going to take etc The classic CF girl workouts are a good place to start. Fran, Cindy, Helen etc to get a feel for how metcons should look and feel. My best advice is keep it simple. 5 rounds for time of 2 movements or for AMRAPS stick to 3 movements. As mentioned above by Braden doing movements that appose each other like thrusters and rowing are a good way to go. People try to overcomplicate them or make them look sexy. There's a lot of dick waving and pandering to client's egos when it comes to programming for Crossfit classes. 40min+ Hero workouts are a prime example of way too much just for the sake of it. Metcons are supposed to be high intensity, so anything over 15-20mins starts to become zone 2 with movements that get super sloppy and end up causing overuse injuries. The more skill required for a movement, the less intensity someone can bring to it. Pat Sherwood talks a lot of sense around programming. Worth listening to him on the subject.