I guess is fair to say that most of our thoughts are not that high quality. However, it’s not to say that there isn’t some good quality thoughts mixed in.
However, how one can recognize a quality thought from the stream of many? Most of the people cannot, and the state of the things reflect that.
To know a quality thought, we must learn to recognize some. Usually success (results) in an area of life or another is good indicator that they must have some thoughts that actually work. Also books for example often have at least some quality thoughts. With the effort of writing a book this tends to be the case, but is not any sort of guarantee.
Thanks to the sheer quantity of thoughts, most of our conscious stream is not quality. In fact probably the best bet is indeed to look for quality thoughts outside: books, people who read book and people who have practiced thinking.
Then also one alternative is to start practicing thinking, which can take a while. And while at it, it might be good idea to write some thoughts down so at least you’ll recognize a good one from the bad one eventually.