As a start, find out about different job titles and career paths. It's difficult for most people to imagine what the duties will be. Meet the people who actually do those jobs. Examples are law enforcement rangers in parks, are superintendents, maintenance staff, or personnel who deal with outdoor recreation activities. However, in some agencies these titles may combine several responsibilities, which may include some direct natural resource work.
Many outdoor jobs require long or irregular hours, some travel, and frequent weekend work.
The lack of time to work on one's specialty can be frustrating at times. For most of these jobs, summer employment, internships, and volunteer work with graduate students or professionals in your field provide opportunities to really understand what's entailed in a specific field. The experience will make you a more attractive applicant, help you to make contacts, and help you get that experience that may be necessary to land that first job. If all possible, accept positions directly connected with your intended field, even if the pay doesn't dazzle you. Also, be willing to go where the work is.