The easiest way to increase the size of your network is to Close the Loop with as many people as possible.
Additionally, when you share, bid, or buy from someone you are helping to close the loop with someone. When you take these actions, you are increasing the chance that the other person will reciprocate these actions with you. Thus, you will Close the Loop with each other!
The more you close the loop with others, the larger your Circle of Trust size and motivation.
Summary: The more people you "close the loop" with, the more people will share your posts and the more you earn.