Cover letter to resume: how to write it competently
The basic information to which the cover letter should be loaded is your advantages over others in the context of the proposed vacancy. Specify, worked exactly in this (or, at worst, in a similar) sphere.
If you can offer the employer a client base or a database of sellers - please specify. Most often, a good base outweighs any experience.
It is not necessary to write down in detail all the experience of working with the school, for this there is a summary.
Leave the contact information in the letter is meaningless, do not overload it with unnecessary information. However, it does not prevent to subscribe if there is an indispensable "Sincerely. ".
Do not forget about the polite form of the letter. At least, say hello before it starts.