FB is good for a few things, but mostly is a time-waster. It is also another way for Big Brother to keep tabs on us -- don't overlook that fact. More don'ts: Don't over-use it, don't over-friend, don't hit "Like" to too many things, don't overreact to any political or religious themes, and don't get addicted, and you'll be alright.
After about 9 years, I'm growing more and more tired of it and try to limit use somewhat. I'm not an addict, but it *is* an extremely wasteful way to waste time, for times when you have time to waste. But I really don't use it now as much as I did before, and thank heavens. It can make you laugh and make you sick all at the same time. The least amount of time you can spend on FB, the better IMO.