it's a lot of hard work and showing leadership in a certain aspect of the site. the best way to start with being part of the staff in general is to become knowledgable and contribute with great posts in the discussion areas of the meta you enjoy, or contributing to Contributions and Corrections by writing analyses. Using IRC is also very important, as you can become friendly with people who are in charge of the sections you might be interested in becoming a part of. Good luck!