Your best source is your own judgement founded in your experience, knowledge, reason, and common sense. Keep learning, listening, talking, interacting; keep on thinking and looking at things from different directions.

Recognize when you are being given a sales pitch. They'll be after your money or your allegence.

Ideas can be viewed as viruses, and in this information age we inhabit, it's like swimming in the kid's pool. One of Stephenson's characters in his book Snow Crash says it well:

"Look. Your brain has an immune system, just like your body. The more you use it - the more viruses you get exposed to - the better your immune system becomes."

(I'd be curious as to what folks here would include in the syllabus of a critical thinking course, but in a new thread...)