Even without an agent, there are things you can do to get jobs on your own. Check the trades for casting calls, and contact casting directors directly. All resumes are not created equal. Always keep your resume current, and remember to include all union affiliations. Submit appropriate photos.
Commercial agents require different types of photos from theatrical agents.
If you have a film or tape of yourself you may want to submit it either in addition to or in lieu of a photo. An audio demo should generally not exceed three minutes. The purpose of the tape is to display your style, quality and range. Always send your submission to a specific person at the agency. Indicate in your cover letter that you are seeking representation and state why you would like to be represented by them.