The Bible actually refers in several places that we should beware, but since this is Advent, we're going to focus on two of the Gospel verses that talk about being on guard against the falsity of men:
Matthew 7:15: "Beware of false prophets, who come to you in sheep’s clothing, but inwardly they are ravening wolves."
Matthew 10:17: "But beware of men, for they will deliver you up to the councils, and they will scourge you in their synagogues,"
There are many other areas in the Bible that use the word "beware" - Bible Gateway is a great place to look things up, and it's very easy to use.
So in your meditation, think about what and whom you need to beware; think of how you will guard against it; think of how prayer might be worked into it.
Activity for the Day: Take food to a food bank. If you're unable to do that, volunteer some of your time to help them out.