I always look for people who have a sense of humor, know boundries, are inoffensive to clients, have the emotional intelligence to read people's moods and understand social conventions and situational awareness, have technical skill, don't bitch, and be able to solve problems. I can teach someone to light a set and use a meter, load 8x10 film, pull focus, etc. I can't teach people how to act. You must also have a leatherman and grip gloves.
We did a recruiting ad for the Marines. On set, which was at Quantico, we had issues rigging lights and scrims in the woods. A lance corporal asked if he could help. We said sure thing, have a go. He got two other marines and they rigged everything up in tall pine trees in about a minute. They humped these lights up the trees, no ropes, it was extraordinary. They hid the scrims in branches. They ran electrics for us off pigtails on HUMVEES. My assistant, who I love dearly and call Maynard because he looks a bit like Maynard Krebs from the Dobey Gillis Show, told me that he and the other assistants felt emasculated. So yeah, I'd like a Marine as an assistant, but a mellow one that likes Rothko, and can edit the language when clients are around.