From Divine Caroline:

Trust is what keeps our society functioning. Evolutionarily speaking, we must trust to survive. But it can be a slippery thing. What makes us trust people? And more curiously, what makes us trust some people but not others?

1. Familiarity. The more contact you have with someone, the more information you collect about him or her. The more information you have, the more confident you can be in your expectations.

2. Resemblance. If someone looks, dresses, or acts like you, you’re more likely to believe his or her actions and reactions will be similar to your own. A 2002 study at a Canadian university showed that people are more likely to trust someone whose facial features resemble theirs.

3. Consistency. The more someone behaves with consistency, the better you’re able to establish patterns and form expectations.

Click off to find the rest of the steps here.