Pick a series of numbers between five and eight digits long. Avoid numbers that contain obvious personal associations: your street address, your date of birth, your cabin at summer camp where you were touched inappropriately by your counselor--these can all be easily accessed by a clever hacker with access to your voter registration or a police report filed in Skowhegan, Maine during the summer of 1986.
Phone numbers of ex-girlfriends are a bad idea--you need to move on, get out there and meet someone, anyone. And there's no shame in using the Internet to date, just to get your sea legs back, buddy. A bunch of my friends used the Internet for dating. Not me though. However, if your ex-girlfriend happens to be a stripper, then it's okay to use her number, but if the phone number doesn't remind you of her, taking $300 in 20s from of the ATM probably will.
Do not write your PIN down. But if you must, put it in a safe place, preferably in a fireproof box or surgically implanted in the healthy liver of a young child. Then create a map to lead you back to this secret place. To insure the map's security, have it cursed by a witch or a high level player on "Magic: The Gathering." Also, remember the code word to break the curse, write that down and repeat this process from the beginning.
Most banks will advise against using your social security number as your PIN. Which is exactly the reason why you should use your social security number. Banks say your PIN should be a special secret given only to trusted individuals. But remember the last time someone you trusted told you to keep a secret? Your parents ended up filing a report with the Skowhegan police department.
And if, after all your precautions, a clever hacker still manages to figure out your PIN and steal your identity, then that's their problem: Let's see how much they enjoy being the 32-year-old Internet dater with a collection of PEZ dispensers and $15,000 in student loans.