[jvm___]

This. Most groups are casual, but they all have their own styles. One is a trail run where we stop every mile or so for a few minute break (if needed). Another is a 'meet at starbucks at 8am and we'll see you at 9am for coffee' where everyone runs their own pace/distance, sometimes shared, sometimes not. Another is hill repeats where walking is also 'acceptable' and we chat at the bottom and top and wait for walkers so they don't feel alone (and we get more time to rest :)

Just show up and try to improve yourself. Be friendly.