by BZ 22-Dec-14 contributor of the Song Lyrics and MP3s in the downloads section)
Nothing ruins a jam more than if people don't respect each other enough to follow a few simple rules when playing together. Here are a few suggestions that will go a long way toward an enjoyable jam. Keep in mind that there's no "I" in "Jam" like there is in "Open Mike". A pleasing group effort is the goal, not trying to impress others.
1. Keep your instrument in tune. If you show up to a jam without a tuner attached to your instrument, it's guaranteed that you will get out of tune as the jam progresses. As a room warms up, stringed instruments go flat, and vice versa. Some instruments are affected more than others, but all will change enough to be objectionable. You should check your tuning after every couple songs. It only takes about 20 seconds, and today's clip-on tuners are sensitive enough to pick up a very gently plucked string. Turn away from the group if you can't do this quietly. If you don't have a built-in or clip-on tuner for your instrument, realize you can have something like a "Snark Super Tight" tuner delivered to your house from eBay for about $10.
2. No "noodling" between songs. Other people are trying to figure out what to play next, so silence your instrument when the song ends. This is especially true for louder instruments like banjos.
3. Don't play or sing over someone else's leads. When someone else volunteers to lead a song or play an instrumental lead, back off on your volume and soloing. Avoid singing melody on top of the lead singer, and keep your playing simple when others have the instrumental lead. Imagine a spotlight that shines on whoever has the lead, and don't try to draw it to yourself when it belongs to someone else. There's generally room at the end of a sung line for a little flourish, but then back off. Listen and appreciate the effort that another is making for the group. Singing harmony is almost always welcomed, but singing the melody over the lead can be very distracting unless specifically requested.
4. Don't force your originals on others. Do songs others know (or should know). Originals are for open mike sessions, not jams. Try to select songs that belong to the genre(s) of the jam.
There are other Jam Etiquette rules easily found on the Internet, so check some of them out. But the simple suggestions mentioned above will go a long way toward making a jam enjoyable for everyone.