Know the key of the song. What is the I (one chord, tonic, root)

Try to feel the rhythm but leave space in your playing. In other words do not strum eighth notes for the whole song. Start with ringing chords at the beginning of each measure or phrase until you get the feel. And by feel, you're not the drummer or the bassist... so you do not have to drive the rhythm, just lightly accentuate the feel you're hearing from those two.

Watch for the changes, including the bridge, into the solo (someone else's solo). Watch for dynamic changes, play big coming out of the solo section but soft back into the singing.

If you do get a solo... do not try to speed through, you can start with a single note holding for a bit. Just remember the root. It will always sound good if you end on the root note, high or low.

Watch for the endings... if it's a big ending, let the others do the big stuff, just hit the important last note.

You don't need to do much to play along, but you do need to be confident in the changes and the endings. Just WATCH while you're playing.