Don't use information related to yourself as a password
Students at a school in London exploited a teacher's poor password selection to access grades and other school records. The teacher had used his daughter's name as a password, but became suspicious when students made reference to an excursion, which had not yet been announced, so he changed his password to the registration number of his car, which was parked outside the school every day. When he received complaints from other teachers about grades being leaked, he changed it again, this time to his postcode. The students in question cracked this within days too.