Well besides from not sharing your personal logins and accepting only friends whom you know, the next best thing to do in order to keep your facebook account safe is also try their "https" and avoiding the use of 3rd party apps..
Always bookmark the facebook homepage, and always click on that. Make sure it always says https://www.facebook.com in your browser. Try not to connect to too many sites which want your Facebook details. Some sites like to use Facebook connect, which is fine, but always be wary of the ones wanting to view your profile and have access to your friends list etc;.
If you want to keep your Facebook account safe, just apply a better password to the account. You can use a password with characters, numbers and letters, but don't forget to write it down as well, so you can remember it if you forget it.
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