Here is a clip of a nice, slow tune of Jenn Bojm's that I played banjo on.
firefly from jenn bojm on Vimeo.
Slow tunes like this one may not scream for a banjo part the same way your uptempo barnburners do but I have found the old 5 string can add some welcome textures and distractions. A few tips from my experience playing banjo on slow songs...
1. Milk the dynamics. On the fast tunes an 'every note loud and clear' approach is often the way to go but when you scale the tempo back the dynamic subtleties really jump out. In my head I try to think of the phrasing more in a sense of how it might be sung and tend to swell in and out of ideas a little more.
2. Listen very closely to everything else on the song. This can be difficult with recording because some instruments will be added after you record your part but I find the more attention I pay to the vocal and the other instruments the better the results.
3. Find the holes and fill 'em. When the singer stops to take a breath that's an opportunity to make some noise.
4. Try beginning and ending phrases somewhere other than the 1 beat. Nothing wrong with beginning on the 1 but a little earlier or later breaks up the predictability.
That's all my advice for today. Thanks to Jenn for writing such a nice song.