I am habitually a solo rider, so this is based on only half a dozen group rides over many years.
- Think of it as just another bike ride, don't get too invested in it. Emotionally I mean; just ride.
- They're likely to be squirrelly by solo rider standards. Not watching ahead for hazards and suddenly veering. Likely paying less attention to traffic patterns up ahead. Talking and weaving. I just give them space.
- If you happen to get caught up in a pace line, not likely in a D ride but could happen, you may be easily strong enough but inexperienced. The same could be true for others in the pace line. Personally I might draft at the back until I can safely drop off without anyone behind me. They don't like it if you make a gap that they have to catch up after going around you.