1. Dress to impress - appearances do make a difference. Since you are 16 you will need to dress "older".
2. Be prepared - when you go in to fill out those applications, make sure you have your pen handy and your resume, as well as numerous references
3. DO NOT LIE - many places check out your references, if you lie and they find out, you'll get black marked with that business and their personnel / hiring team
4. Try to take the experiences you have and make them relate directly to the job you are applying for.
Example: My familiarity with Word, Excel and Power Point will aid and assist me in producing high quality work.
My work on the school year book has helped me hone my organization skills that will allow me to get things done in a timely manner.
5. Spelling counts and so does neatness - if you are filling out an application by hand, go slowly, think through your answers first and then print them in your best handwriting.
6. Be polite and sweet - If you can leave the application with a person who has a smile on their face then they'll put you on the top of the pile. If you bring that person down your application could end up in the trash.
7. Be clean - Have minty fresh breath and smell nice but not overwhelming (too much perfume isn't good either). Remember the person taking your application will probably be thinking "do I want to be next to this person for long periods of time".
8. If you get the interview, send a thank you note after the interview is over.
(those are off the top of my head)