Work with organisations already working with those groups. Talk and listen to what they have to say look for areas where your ideas converge. They may not necessarily be where you expect. For example you might approach an LGBT group with the offer of a creative arts project but find that they are interested in work experience. Be realistic and honest about what you can offer but look for the link ups. There are lots of groups so don’t be deterred if the answer is no after a bit of door knocking you will find some friend.