Always sing as loudly as possible.

If you get lost, turn to the person next to you & point at a specific spot on the page of the lyrics.

If you do not have lyric sheets, and you get lost, smile broadly and mouthe the word "watermelon" repeatedly, being sure to take a breath when the others do.

Be sure to bring your Banjo & strum along.
OR:
Be sure to bring your Bodhran & tip enthusiastically during all the singing.

If anyone infers that you are singing off key, pull out your battery powered tuner, hum into it, & state loudly, "See, I'm exactly right!"