To avoid a great deal of confusion, avoid the following characters in your passwords:

Upper case "i"
Lower case "i"
Lower case "J"
Lower case "L"
Upper case "o"
Number "1"
Number "0"
Examples:

lI1 - This is the letter "L", the letter "i", and the number "1".

O0 - This is an uppercase "o" and a zero

ij - This is an "i" and a "j" underlined.

Always remember, it's better to highlight the password, copy it by right clicking and paste it into the login screen. That way, you wont have to figure out what the letters and numbers "really" are.