I also believe that the things we are exposed to and take in are constantly changing and influencing us, and your question is a very good one.
I'd say the first and most important step is actually realizing this and being mindful of your surroundings and what flows into you. After that, it would probably be pretty personal what you consider beneficial and approve of it. Things we don't want flowing into us, we'd have to recognize them, then take steps to lower their impact on our lives. We probably cannot get everything, but even a little mindfulness can help a lot.