I think social activities that don't involve alcohol are good. Clubs, volunteering, outdoor activities, exercise classes. I look for activities where other people go by themselves more than family or couple type activities. I also look for activities that normally involve social interaction. Lectures are okay but if you spend most of an hour listening to the speaker, there's not much time for asking the other participants how they like the activity, how long they've been doing it, blah, blah, blah.