Young people for starters. Most people who ever come to faith do so before they leave their teen years. Do a little survey in your class. Ask how many came to faith before they turned 20. Also, people who have gone through some kind of change-a move, a new baby, etc. tend to be more reachable.
Young couples are often receptive just after the birth of their first baby.
New move ins to the community are a hot group. The hottest group, that is often overlooked, are the people who visit your worship service. That is, very few of those visitors stick around. Most churches could grow just by taking real good care of the visitors that visit. Also, but doing this, it tends to increase the number of visitors because these people know outsiders they can invite.