A recruiter does not like to be surprised. Be prepared to give references from your last three employers. They should be people who supervised you or had direct knowledge of your work product. A recruiter might ask you to rewrite your resume to emphasize skills needed for a current opening. When an opening does exist, the recruiter will provide you with background information about the employer and the position.
Employers offer salaries based on skills, years of experience and current salary guidelines.
It is in the recruiter's best interest to get you the best offer possible. There is always a chance that you will receive a counter offer from your present firm. Discuss this possibility with your recruiter before you begin the interviewing process. A recruiter's time is valuable. If you use a recruiter and the recruiter's client to increase your leverage for a raise at your present job, you will burn two bridges in the process.