Human-memorisable passwords tend to be weak. This problem and its solution are best demonstrated by the following XKCD webcomic:
The solution is to use a good, random-word password.
It is also clever not to reuse your passwords across all sites as you never know which one gets hacked (a single compromised account could leak all the passwords ). It is better to have more passwords, preferably different one for each site. You can write down your passwords into paper on your desk or use password manager which remembers passwords for different sites and secures them under master password.