LinkedIn Groups
Looking at what people are saying about LI groups, they seem very much like Facebook Groups. If you join a few you will need promotional strategy to use them effectively. This will most likely be posting about work you have done, or a project you are working on. Whilst keeping an eye out for people looking for help. This may help promote yourself within these groups.
A majority of people in these groups are passive users. This means they are in the group, may like a few posts, but otherwise do not engage. This is an untapped market. These people are most likely looking for people to work with. Sharing blogs, making a few posts, will attract these people to connect.
You can find groups via a keyword search. Once in a group you can begin scanning posts and getting a general feel for how each group operates. Some groups will be more active than others. These more active groups with higher membership will be more likely to yield positive connections.
Try not to connect with everyone in the group, this may end up with you being kicked out of the group. This is because they are mainly forums for discussion. The best outlook is a few passive weeks of study, then begin a posting and response campaign in these groups.