Any word, even in other languages, with a number at the beginning or the end. 75sexy genesIs00 Names from the Bible, mythology, history, or literature. Many people choose these, thinking it would be obscure, but they can be cracked very quickly. MarkTwain Keys which are in a line on the keyboard or clustered together in the alphabet. Anything less than six characters is easily guessed.
Many providers recommend eight to twelve characters.
Using upper and lower case helps a little, but not as much as you may think. To be truly secure, you really need to choose a random selection of letters, numbers and punctuation, and consider changing your password about every three months. Choosing a random looking password doesn't have to be as hard as it sounds. For example, choose three words, and put semi colons or numbers in between the words. Use two or more words or names, and misspell them.