I've written a zillion, and still counting. 🙂 Here's a few tips:
1) Limit your cover letter to a page. HR doesn't want to read a novel about your life.
2) Don't just simply repeat your resume in your cover letter. The cover letter is for you to express your intrest in the position, the company, and explain why you are an excellent candidate.
3) Be enthuiastic in your cover letter! Sound like you REALLY want the job and that you are THE best. Don't go overboard though. 🙂
4) Save your cover letters! You can constantly upgrade them, or taylor them to specific job apps. They'll improve with time.
5) Structure: your cover letter should be structured as follows:
Header:
Your Name
Your Address
Your Email
Phone
Date
Choose a greeting: To whom it may concern; Company Hiring Manager; Name (if you have it):
Paragraph 1: Introduction - Tell them how you found out about the job, what job it is you are applying for, and that you would be an excellent candidate for the position.
Paragraph 2: Main body - Express why you feel you are an excellent candidate for the position. Highlight achievements (spare them the gory details), experience, and why you desire this career shift. Use wording/buzz-words from their job description in your cover letter. Quantify ANYTHING you possibly can. This goes for your resume as well. People like to see the results of your work, not that you simply did a task.
Paragraph 3 (could be included in paragraph 2) - Use this paragaph to speak of personality traits that make you the ideal candidate. "Failure is not in my vocabulary", "I am a team-player", "Natural leader", "I set high goals and seek to acheive them", "Self-starter" ect. Use ANY wording like this that you find in their job description. Remember...You ARE their job description!! 🙂
Paragraph 4: Concluding statement - Express why you desire to work for their company. Again state that you feel you are the perfect candidate. Thank them for their time. Arrange to follow up if you have contact info. If you don't have any contact info, instruct them to contact you at their convenience.
Hope this helps. Write your first draft, post it. We'll critique. 🙂