In general I think it's good to be in touch with communities centred around your language and framework to get a good idea of how people are solving similar problems to yours. Things change so much over the years and there are multiple ways to solve the same problems that you won't get from just reading official documentation. Once you get a sense of the general playing field you can deep dive into certain topics.

I can't speak for other languages and frameworks but I know with Android Development it's useful to keep an eye on the subreddit (https://www.reddit.com/r/androiddev/) to see what the latest general consensus is with libraries and frameworks. There's also a #android-dev channel on Freenode IRC that I dip into from time to time. Meetups are pretty good too, and people tend to enjoy conferences although personally with my poor attention span I tend to switch off. There's a weekly newsletter as well which I find really useful (https://androidweekly.net/).

No idea what the equivalents would be for Node + Express and MongoDB but I'm sure they exist :).