Anyone who's serious about success understands this truth: the people in your circles determine your trajectory. It seems like a simple concept, but it can seem remarkably difficult to curate the people you spend time with, considering your family members and people you work with can seem like factors outside of your control. But according to Ivan Misner, Stewart Emery and Rick Sapio, authors of Who's in Your Room? The Secret to Creating Your Best Life, you're the only one who can ensure that the people you spend time with are positive influences.

Your life is one room

The mind trick they put forth is this: Imagine that your entire life is lived in one very large room (as big as an auditorium) and its one door only leads in. Everyone who comes into your life can never leave. Of course, in real life people do come and go, but when it comes to your psyche, everyone who enters "your room" leaves a permanent imprint which affects your daily experience.

Think about your positive and negative emotional states

The book's authors suggest thinking about the times when you've experienced harshness and anger, as well as when you've felt love and kindness. Who are the people playing into these states? Even if you can't remove someone from "your room," being aware of how people influence you can help when it comes to setting boundaries.

Create an imaginary doorman who screens the people who want to come into your room

First, though, you need to identify the key values your doorman needs to be aware of. Then, when people ask something of you, you can mentally discuss the matter with your doorman who will remind you of your list of values so you can commit or decline accordingly.

Get better at saying no

You can do this gently by telling someone you don't have the time or expertise to do a good job. You can also point them in the direction of another person who could perform better than yourself. Or, offer a different solution.

Increase the number of mentors in your room

The authors suggest creating a two-column list. On one side name all the people who are positive forces in your life and enhance it personally, professionally or spiritually. In the other column identify at least one thing you can do to fortify each of these relationships, whether it means spending more quality time with the person or inviting him or her to lunch or coffee. "Then pick up the phone, send the email, or attend the social gathering," they write. "Take steps today to strengthen your relationships with mentors by engaging them and, when appropriate, expressing the value they have in your life."