Pick companys that you use and like their products. In my opinion I would only be with a company if I truly believed in their products and service. Compile a resume of your accomplishments and skills. About one page for a cover letter and one page for your resume. Keep it short and to the point highlighting your best points. You will be wanting to showcase what you can do for them not the other way around. You will want to build it just like you were applying for a job with them. Include your best hunting and shooting pictures. That will atleast get you started. Probably the best bet at your age would be to hang out at your local shop talk to them, help out when you can, and start through them. Then work your way up to the larger companies. Remember there are thousands of other people wanting the same thing as you so you need to stand out above all of that. Start small and don't get discouraged. Conduct yourself in a very profesional manner at all times.
Thats just a little bit of it to get you started. Hope this helps some.

Craig