On the MBTA they have automated stop announcements like:

Next stop: Porter Square. Doors will open on the left. Change here for bus connections.

While it's somewhat useful to know there are buses you can take from Porter Square, that's not enough information for someone to go take one of them. Worse, since there are bus connections at every subway stop, it just annoys people and they tune it out. It would be better to have:

Next stop: Porter Square. Doors will open on the left. Change here for the 77, 83, and 96.

At stops where there are a lot of buses you might just give the key ones:

Next stop: Harvard Square. Doors will open on the right. Change here for the 1, 66, 71, 73, 77, and other buses.

Alternatively, since not everyone loves bus numbers as much as I do, you could think about what areas are most commonly reached by transfering to a bus here and announce those:

Next stop: Harvard Square. Doors will open on the right. Change here for buses to Allston, Watertown, and other destinations.

Note that this requires local knowledge, and it's not just something you can generate from a list of bus routes and their final destinations. For example, the 66 runs to Dudley, but that's far enough that if you're on the Red Line and want to go to Dudley you should go downtown and take a bus (SL4, SL5, 47) from there. But the 66 also runs through Allston on its way to Dudley, and is a very good way to get from Harvard sq to Allston, so we should annouce that. I guess you could generate something like this by seeing which buses Google Transit tends to recommend people change for at which stations? This would be somewhat better than looking at which transfers people currently do make, since there probably are good transfers people could be making if they knew about them.

Here's examples for what this could look like for the north end of the Red Line:

stop	full bus list	"important" bus list	destinations
Alewife	62, 67, 76, 79, 84, 350, 351	62, 79, 350	Bedford, Burlington, Lexington
Davis	87, 88, 89, 90, 94, 96	88, 89, 96	Arlington, Medford, Sullivan
Porter	77, 83, 87, 96	77, 87	Arlington, Lechmere, Union
Harvard	66, 68, 69, 71, 72, 73, 77, 86, 96	66, 71, 73	Allston, Watertown, Union
Central	1, 47, 64, 70, 83, 91, CT1	1, 47, 70	Fenway, Hynes, Inman, Waltham
Kendall	65, 88, CT2	85, CT2	Sullivan, Union

Now that we have automated stop announcements there's little reason not to customize them per-stop to make them more useful.