Multiple Passwords
VERY IMPORTANT: Never use the same password across all sites you register on.
Although it is easier to remember one password, if a site leaks your login details through a security breach, the information maybe tried across other common sites such as banking sites.
When registering on a site try to keep a different login password. As it would be impractical to remember ever login, try a password based on a variant of the site name. For example you could have a common strong password such as $tr0ngP4SsW0rd. Then when registering use a part of the domain name either as a prefix or suffix. For example, let take the first 3 characters of a domain and prefix it to our $tr0ngP4SsW0rd. For example, when registering on www.ebay.co.uk we would use the password "eba$tr0ngP4SsW0rd".
Never write down your different passwords unless absolutely necessary. If you do need a record your passwords then you could try the various password safes available such as Password Safe.