1. No Personal Information. Any novice hacker can easily find out your full name, the names of your spouse or children, your pets, or your favorite sports teams. Never choose a password that has anything to do with you personally.
2. No real words. Let's take that a step farther. Not only should you not use your name or your pet's name, you shouldn't use any actual word that can be found in a dictionary. Passwords like that can be easily cracked by password software.
3. Mix Character Types. Passwords are almost always case-sensitive, so use both upper and lower case letters to make it more difficult. To really make it complex, be more creative than just capitalizing the first letter. For example, do "paSswoRd" instead of just "Password". Better yet, throw in some numbers and special characters to substitute for letters, and do "p@Ssw0Rd".
4. Use a Passphrase. Scratch that. Some password cracking utilities are also smart enough to use common character substitutions for common words. Cracking "p@ssw0rd" may take longer than cracking "password", but it will still be relatively trivial to crack because, special characters or not, the password is still "password".
Instead, take your favorite line from a movie, song, or book and convert it to a passphrase. If you like the scene from A Few Good Men when Jack Nicholson is on the stand, take the line "You want the truth? You can't handle the truth!" and convert it to "Ywtt?Ychtt!". It has upper case and lower case letters, as well as special characters. It is not a word appearing in any dictionary, yet it is simple for you to remember.
5. Use a Tool. The main reason that users choose passwords that are easy to crack is that they want to choose passwords that are easy to remember. It is obviously much easier to remember your dog's name, or type characters in the order they appear on the keyboard, like "123456", than it is to recall "a5$jgFD118@Kle45@". But, guess which one is more secure?
Source: PC World