In your letter, first and foremost you need to introduce yourself. Next, you need to give the highest qualification or the degree you have and the expertise you have. This should be in no more than two sentences. Lastly you provide a glimpse of your experience, where you must mention the various industries and domains that you have worked for. Also, you can provide the renowned companies you have served. However, do not forget to mention the various technologies that you know. In this letter you must mention you strengths in work area such as compatibility, or communication skill or fast learning capability, or ability to deliver under stress. Having provided the glimpse, mention you contact information and anything else that you want to convey to the addressee. Along with this letter you must attach your resume where all the details about your career is mentioned from the day you started your career till recent.