3) Do not invest or gamble away your bitcoins with any service or person who guarantees returns
This bears repeating, since it's a significant source of loss for new members...
If you see a post or website promising any return (even 1% a day), stay clear. They are called ponzi scams, and they will take your coins and run.
If it sounds to good to be true chances are it is. Many ponzi scams will have amazing offers that no one could actually do. Use common sense.
Also be cautious when someone recommends something with a referral link. It might be great, but they have a reason on recommending it to you.