The letter should be brief, set out who you are and why you are the best candidate for the job. Do not start needless to enumerate its merits, the employer is interested in the facts.
In the absence of information about the employer (name, position), you should call and clarify this with the firm. If for any reason you do not succeed, then you can use the following treatment, for example: "Dear employer."
It is advisable to try to maintain unified writing style and summary. The scale and font possible are the same. You are trying to convey to the employer that you are the right person who is worthy of this post. The letter in turn suggests you, so you should emphasize all the details.
You should not unnecessarily abuse the word "I". This can lead to monotony and recapture the interest for further reading. Replace such combinations as "I am capable, I did, I know how." Write better: "have the ability" etc. This will make the text richer.
The letter should briefly repeat the summary, describe the most significant skills and abilities. One should not lose sight of your personal characteristics, the employer must have an idea of your potential. You should also give a description of the most significant achievements. Depends on the company's interest in you.
At the end of the letter, many make a common mistake - write the sentence "Thank you for your attention, I will wait for the answer." This is not necessary, as the answer, most likely, will not follow. Complete the letter with the words: "Thank you for your time. I will contact you (date and time), and we will discuss when you will meet up with me."
At the end of the letter do not be lazy to read it, and better to do it a few times. Perhaps the text has gaps and errors. Remember, this letter depends on the first impression of the employer, this is your chance to fill the offered position.