This question has a pretty simple answer that might expand into something complicated, WE WILL SEE. Basically "the right choices" are, when you get down to it, "the choices that lead to a future I want" -- I was going to add "and doesn't paradox me out of existence" but I'm pretty sure he's far enough out of his timeline that that's not going to be a factor. (Which is good because he definitely shanked both his parents.) But the complicating factor -- I knew there'd be one -- is that that future only has to exist -- and time streams branch and coexist with each other. So what he's actually doing is pruning a branching decision tree very carefully so that the outcomes he wants are statistically likely. He doesn't have to go as far as forcing them -- as long as they could happen, he can follow them down to the next.

Tsalalagal mentioned that Marethyu and Abraham were in the business of promoting Auspicious Threads, timelines which had an unusually positive outcome, and I think Josh would still do that now that Marethyu has accomplished his goals. In general, he wants to give timelines where outcomes are good (for humanity in particular, as a whole) the best chance they can to prosper -- I suspect that there are levels of existence to timestreams, and that they can re-merge or become less "real" or otherwise order themselves by precedence. Universal quantum physics is complicated! But there's a concept of a timeline that's "dead"/"impossible" and ones that are more "alive"/"possible" than others.

The point of that digression is that Josh wants humanity to prosper in general, and wants the modern world he came from to exist in specific, but it can be said to exist as long as it lies down a possible path of decisions. So what he's curating are a) that that possible path exists, so Sophie has something to go back to and b) making futures where humanity prospers more likely.

In terms of in general life, Josh pretty much doesn't consider that he has any idea what the right choices are. He thinks we decide what's right for us every time we make a choice, and he's pretty sure that everyone has to do that for themselves. He hasn't really thought about this a lot, though. It's kind of overly philosophical for him at this stage of his life.

...okay, we've been talking about this all evening but seriously, talk to me about Mau and Edmund.