The resume and cover letter you submit must demonstrate and display your "best" work. Would you hire yourself if your resume were in a stack of 1000 others? To ensure professionalism, send a cover letter, and address it to the hiring manager. Make sure the spelling of his/her name is correct. Do not fold your documents - send them in a full-sized envelope. If you are unable to personally deliver the resume, send it by overnight express to make a great first impression. There must be no typos or grammatical errors. Remember, this is an indication of your best work.
There are many tricks to writing an effective resume. The most important fact to remember is:
Write your resume to sell YOU - consider it a critical marketing tool