Google maps doesn’t always have good data for transit.
Another option is the app Moovit. It’s served me well in Latin America. I’m also trying out Organic Maps and OsmAnd, which are Open Maps apps, but I can’t really comment on them yet.
The only catch with transit directions in apps is they’ll often have bus numbers, but the buses here have signs for the neighborhoods they go through or the final stop, which makes things tricky, especially since you’re trying to read the sign while the bus is moving.
I like Moovit, but since it’s a tracker and battery nightmare, I have to freeze it when I don’t need it. Other than that, I think it does probably the best job it can. If you can’t read the bus, get on and ask the driver, showing him the app directions.