The bad guys use dictionaries to compile lists of possible passwords to use when breaking into a computer system. Even adding digits or punctuation may not add to the security of your password unless you do it in a random way. Appending a dictionary word with a digit or punctuation mark is probably as insecure as the dictionary word alone. Instead, use digits and punctuation in surprising, creative ways. And, just capitalizing the first letter is not nearly as helpful as using a vAriEtY Of mIXeD cAse leTtErs would be.
Some experts recommend using misspelled words.
But, again, you must be careful not to misspell your words in a predictable way. Coming up with a good password takes some time and thought. Fortunately, many of our systems give you a few days warning before a password expires. Use this time to think of a good one and then make the change. If you wait until the last minute or select a password in haste it won't be as strong as it could be.