Another thing people should be aware of is 'like farming'. When you see those pages come up with stupid quizzes like a word-search that says 'what word do you see first' or 'click here and watch what happens' or 'hit like when you spot the mistake' etc, or those photos that use some heart rending story and say 'click like if you support this child..' - those pages are very often gathering 'likes' so that they get millions of likers, and then they can sell the page on to someone else, who can then replace the content with whatever they want, and it will seem like the page/photo/etc is really popular, when actually people have been liking or sharing something completely different and have no idea that they're associated with whatever it is.
So like and share stuff from friends, or from reputable sites/pages, but not all those 'what is the first word' things, or the stories that sound tragic and heart-warming, because there's a good chance they aren't true anyway and might be just being used to get 'likes'.
It's also why go after someone who has 'liked' a dodgy page like this one isn't a good idea, because they may or may not have actually known that is what they were doing, if the content was changed after they 'liked' it. Better to let authorities investigate and sort things like that out.