personal statements. having helped several people with theirs and toiling through mine which I feel is the best thing I have ever written. A few (ok a lot of) points.
1. Be succinct in everything you say, but not too succinct.
2. Use normal language - do not try to impress them with jargon, do not get all romantic, you need to conserve space and be efficient
3. if the sentence is not making a point or supporting a point, can it!
4. 500 words is typically the unofficial limit, as thats about 1 page single spaced. treat this as a resume - number of pages is inversely proportional to how interested they are in it. If you give an HR person a 10 page resume, they will kindly show you to the door.
5. talk about what would make you a CAPABLE doctor, not a great doctor or any of that - you dont know if you will be one or not. your goal is to save lives, not be americas top physician (i mean that can be a goal, but keep the main goal in sight here).
6. what in your life has made you choose medicine? dont say lifestyle, pay, any of that. its a nice benefit, but be real about it.
7. what qualities do you have, and how can you explain through example? examples are key to this thing, otherwise you are just rambling. If you put your money where your mouth is, you get a better response
8. Do not, whatever you do, be negative about anything. If your GPA sucks and you have awesome EC's, well, your willingness to serve got the best of you at times. it happens, cast a positive light. If freshman year was awful, you grew up (and you need a trend to prove this, once again examples)
9. make sure you proofread this thing about 8 times, have 5 friends PR it, and print it out and read it aloud before you send it. if you dont like something, the adcom wont either.
10. relax. its a personal statement, its you. Can you answer the question "tell me about yourself"? if you can do that, you can write this thing. Make many many rough drafts, find out what you like, keep everything you write in some folder.
11. write it, edit it, leave it for 3 days and come back. its amazing how critical you can be of yourself then.
12. if you are tight with an english prof and an older pre-med type prof (the real hardass bio prof is good) then ask them if they would be willing to critique it. If you can get that, you are golden.
13. Get off of this forum and start writing! you can never be too early.
Good luck, and focus on #10, its the best piece of advice you can get.