Reliability can be a very arbitrary attribute to building a career. My short advice to you is anything will be reliable based on your passion for doing what you are doing, being professional, and continually learning your craft (never think you have nothing left to learn). So, being a documentary film maker, if you are tenacious and just start creating shorts to hone your skills, your style, your voice, you can't go wrong. Check out these film makers on youTube for great advice and guidance:
So keep shooting and improving. Partner with others that have more experience. Take jobs that will help you learn something that will build your arsenal of technique, and stay true to your vision. The money eventually comes, but when it does...you most assuredly want to be doing the thing you love, rather than something to just make money.
Last thought, it is always super helpful to have some knowledge of business, not just the film business. The more savvy you are, the more you can grow your film making brand and business. It also puts you in a position to know how to negotiate and run your own shop.