However, s/he isn't smart enough to discover new knowledge in most fields, or contribute very much to a conversation of more knowledgeable experts on a given topic. Let's assume s/he has no exceptional talents in any area.

Most people are intellectually near-average or below-average, and I have not seen extensive discussion on how to help them lead happier lives that make the world a better place.

Upvoted for caring about other people. Most of your suggestions I agree with and there are some other good ones in the comments. I want to point out that the advice given is pretty much the same it would be for most people anyway. Most people one standard deviation or more from average are also not likely to discover new knowledge either. I believe it is a matter of execution; practical advice is fitting for not-so-smart people and smart people alike (for the most part), whether you can get it done is another matter and smart people usually do, that's why they are smart/consciousness.