There are lots of paths into conservation work, and all of them are good! I personally got my start moonlighting as an NPS volunteer while I worked concessions in Yellowstone National Park, and then as a trail crew lead. If you live in the U.S. and have the option, a position with a conservation corps is an awesome way to get started - you generally don't need any experience starting as a crew member, except for willingness to work hard and some familiarity with hiking and camping. There are conservation corps programs in every state, with a huge variety of project work/living arrangements/term length. The Texas A&M University job board is a great place to look for openings!