Meet New People
To bring new thoughts, ideas and perceptions into your life, get to know someone with a different perspective, occupation, background, culture or religion.
Why? Hanging out with like-minded people is a good way to hear constant reinforcement of your own thoughts and beliefs. This also makes it easy to fall into "groupthink" and makes it more difficult to see (or acknowledge) faults, shortcomings and falsehoods of our own.
That's not to say you need to get rid of old friends -- just spice up your life with some new ones. New friends and acquaintances increase the odds that you're introduced to new ways of thinking. You may be pleasantly surprised to have your worldview rocked a little bit by a simple conversation with somebody who views life much differently than you do. The great thing about widening your social circle is that new friends can help expand it even further by introducing you to people you might otherwise have little opportunity to meet.
You don't have to travel to exotic lands to meet new people who think differently than you do -- in fact, they're all around you. It may just be a matter of being willing to initiate conversations with people from whom you'd normally shy away.
Next: change the way you think by changing the places you think.