The biggest help one can probably be to the project is to create or improve user-facing software. OsmAnd is still clunky and ugly to the average person coming from FAANG Maps, for example. The iOS version is even worse. Some alternative apps exist with better UX, but they're often missing features. There are also some web projects out there that aim to be a google maps website replacement, but none of them are quite there.

It could also be a niche thing, like if you make an app that shows the nearest defibrillator or other emergency facilities that people might need in a pinch. Any area gaining good coverage of this type of data would immediately have an app to turn to. With adoption also comes the influx of new contributors.