Do not choose a password based upon personal data like your name,surname or username, or other information that one could easily discover about you from such sources as searching the internet.
Do not choose a password that is a word (English or otherwise), proper name, name of a TV show, name of a singer, keyboard sequence, or anything else that one would expect a clever person to put in a "dictionary" of passwords.
Do not choose a password that is a simple transformation of a word, such as putting a punctuation mark at the beginning or end of a word, converting the letter "l" to the digit "1", writing a word backwards, etc. For example, "password,123" is not a good password, since adding ",123" is a common, simple transformation of a word.
Do not choose passwords less than 8 characters long or that are made up solely of numbers or letters. Use letters of different cases, mixtures of digits and letters, and/or non-alphanumeric characters. For example : R@Ih2k:Sa&J