There are two things that you can do to make your password difficult to crack:
1) The longer the better. 8 characters is the minimum you should use but 12 is better.
2) The more different elements the better. Use numbers, lower case letters, upper case letters and, if they let you, special characters. (commas, spaces, parenthesis, pound signs, etc.,)
One trick that can make your password easy to remember but hard to break is to make it a word, or phrase and substitute characters that look like the correct letter.
Example: goshopping is very easy to break. G0 Sh()pping is extremely difficult.