Forums and groups
Hanging out in forums or groups and contributing to the debate is a good way to build backlinks, recognition, and trust. It can be very time consuming and often frustrating work as, more often than not, given any 20 people, there will probably be 20 different opinions (sometimes more) about a topic that should be straightforward.
A lot of sites combat this information overload by allowing people to rate answers. This means that, in general, the best responses bubble up to the top of the list. If you are answering questions and helping people, make sure you write clearly and in a friendly tone at all times. If you are asking questions, be sure to offer thanks and appreciation to people who have genuinely helped.
Depending on your niche, you might find that there are quite a number of popular forums or groups to join, or maybe only one or two. Before joining a forum, look at what the community has to offer. Don't join a group or forum for the sake of it.
Note
Everything you...