A well written personal statement can be a crucial ingredient for an application. It could be the single most important factor in getting you an interview invitation (as happened for me), and it could even make program directors see above pitfalls in your application such as bad scores, attempts etc.

There a few basic principals in writing a good personal statement:

1. Spelling and grammar - a spelling mistake or bad grammar can really screw up your application. I mean, come on, how serious can you be if you fail to check spelling and grammar in a document so crucial to your future?!

2. The personal statement is the only opportunity you have to sell yourself for who you really are, unrelated to the cold data in your CV such as scores, past experience etc. Therefore, do not repeat any information previously described in your CV and the work experience and education sections of the ERAS application. I like to call it "The personality statement" because the statement’s focus should be on your personality (it's good parts, of course).
High light your strengths, using as less of clichés as possible. Emphasize the parts of your personality that you think are suitable for the residency you are applying to.

3. Focus on the specialty you are applying to. Remember, there is no one personal statement that will fit all residencies. Each residency has unique virtues and characteristics that make special personality types to choose them for their life profession. The only thing that all of the residencies share in what they want to see in a resident is the ability to work as a team member. Always remember to mention that you "have always been a team player" in your statement.

4. Focus on the program. Yes, I am not joking. Relating to the specific program in your personal statement is something that could really make your application standout from all of the other applications. Read carefully through the program's web site, search for the program director's research interests, the program's special features, the areas special features, etc.
Although it could be a nerve wrecking job to write a hundred different personal statements, remember, this is your life we are talking about. You spent years in medical school and thousands of dollars to take the USMLE steps, and now that you are finally applying, this is the time for one last push to achieve your dream.

5. Make the first paragraph appealing for the reader. Remember, you are selling yourself here. If you want the "buyer" (e.g. the program director) to "buy your product" (e.g. you), you have got to draw his/her attention. To keep them interested. I started my personal statement with a story from my electives and then tied it with the specialty and in the program.

6. Be yourself -this is the best way. If you try to be someone that you are not - it will immediately reflect in your statement. Don't make up things about yourself, don't lie.

Finally, here are some links to sites that help with personal statements:

http://www.accepted.com/medical/residencyessays.aspx
http://www.usmleweb.com/sample_personal_statements.html
http://www.thedoctorjob.com/careerco...?id_article=14