The basic function of a CV is to present relevant information about yourself to the prospective employer. Though the definition sounds simple, there are a lot of angles to the presentation of a CV or curriculum vitae or biodata as is commonly known, which mostly depends upon what type of a job you are applying for. However, whatever be the type of the CV, the basics would remain constant. A good CV:

A good CV should :
Be preceded by a neat cover letter which is addressed by name or authority (designation) to the person who is in charge of recruiting or the chief of the organization (be careful here that you have right name, it is spelled right, and has the right and exact designation); the cover letter should summarize in two-five lines why you think you would be fit for the job showcasing your best talents to match the requirements of the job (and add a little extra)
Represent accurately all the relevant to the job information (personal and professional).