It's 99% networking, maybe 1% luck. You should have lots of hours in the types of aircraft you are looking to fly in. It can be anything, from single-piston to jets. Once you build a relationship with a customer, they switch to bigger and better, they could bring you along. Most of these types of employers don't do a lot of flying over-all, so they don't want the expense of having a full-time pilot on their salary, multiple clients are what will carry you.

This is a very open field, and lots to learn, so it's just like anything else in the aviation world. Plus I can't give away my secrets, as I'm exploring this option myself.