At the bottom of a route or stop's Arrival Times screen, tap the "Favorite this route."
To un-favorite a route or station, simply tap the same button again from the Arrival Times screen.
"Favoriting” a route makes sure that it always appears at the top of the Home screen. Given that transit systems can be quite different from each other, users can favorite routes for some systems, or favorite stops and stations for others. For example, Swiftly users can favorite any bus or train route on San Francisco's Muni; users can favorite stations for the SF Bay Area's BART system.
In the list of "Nearby Favorites" at the top of the Home screen, routes and stations will be listed in order of proximity.