Depends on who exactly you are writing to.
Dear <name, sir, madame, or title (like director)>
I am writing to.... <or> I write to present <or> I submit this application...
:: these may infer that you will soon meet imperson, and that you will say hello then. I usually end letters like this with
..I am looking forward to making your acquantance at your earliest convienience. Please respond by mail, telephone, or email....
If, however, you are applying for a job in which you may never meet the employer in person before being hired, however, you may want to ad a hello, 'greetings,' etc. etc. at the beginning of your letter. If you do say hello at the beginning, it will convey a familiar tone; is that what you want?