We're always asking the full-time missionaries what we can do to help them. They almost always say, "Just be on the lookout for new people and say hello to them." We normally do this anyhow, but the fact that they always suggest the same thing makes me think that there is still room for improvement in this department.
Personally, I get a little busy with the kids (especially during Sacrament meeting, when I usually end up out in the hall), so I'm sure I don't do everything possible to make visitors feel welcome. I know that there are some Ward members who are already pretty good at being "on the lookout," but what if we all did just 25% better? How much more welcome would visitors/investigators feel?
Having personally experienced being new in a Ward many times, I'm fully aware of how awkward it can feel. And I'm a member, so a least I know the routine - must be much more foreign and intimidating for a newcomer. I try to remember back all those years ago to when I first attended church. I don't think I felt that awkward, because I was there with a friend and her family, but I do remember how friendly everyone was!