So I have a question about how some of you folks approach playing along with
songs that don't necessarily have a harp part in them.
The best recordings to learn from and practice with are songs that don't
have harp for you to try to copy. Make up your own part. That's the job,
anyway, unless you play exclusively in cover bands.
This is a perfect opportunity to really understand the groove of a song.
(The groove being the insistent rhythm of the backing track, in case
there's anyone who needs a definition that'd be useful in this
case.) First play with the track until you have a feel for the rhythm
pattern. Then try to find the holes in the pattern where nobody is
expressing the rhythm - maybe one hole, then a second hole, then three or four.
And practice hitting those holes. Once you can do that reliably, find a
nice melody or pair of notes to fill those holes with. Four holes,
four-note melody. After you've got that, sniff around for bits in the
groove where you can play a note that harmonizes with another instrument
within their pattern. Practice constructing parts for yourself in this way.
There are usually several grooves on a track, say perhaps one for the verse
and one for the chorus. Sometimes more. See if you can't find a way to
fit in everywhere.
This is a great thing to practice on tracks that don't have harp already.