We've all seen those ads or links on Facebook: "click here for a free iPad" or "like this for a free Tim Horton's gift card". Hopefully you've never clicked on them (or any of the "OMG! I can't believe what this girl did" links). They are scams, 99% of the time. If you're lucky, you're just taken to a website trying to sell you something. If you're unlucky, you're click-jacked or worse.
I'm always amazed by the number of my Facebook friends who are taken in by these scams. Or who share information that they saw on their friends' pages without confirming the truth behind the rumours. Please, take 30 seconds before you click "share" when you read something on Facebook. And NEVER click on any video link that starts with "OMG". You're just asking for trouble.
The best source of information about these scams (at least, in my opinion) is Sophos. Look them up on Facebook, and "like" their page. They give up-to-date information on the latest Facebook scams (like the free gift cards, the video links, the idiotic memes, etc.) and can protect you from looking like an idiot or getting a virus.
Another great spot is Snopes. This is where you can find the truth about all those memes that your friends are trying to spread (e.g., fake Amber alerts) as well as a ton of other information about scams.
If it seems too good to be true, it usually is.