Listen to opposing ideas and develop your own ideas, methods, and thought-processes. If you’re conservative, listen to liberal ideas (or vice versa). Don’t just hear the “opposing side” talk; listen to the message they are trying to convey. Be open-minded and really try to understand where they are coming from.
Why are they proposing that idea/solution? Find at least one positive in every idea that you hear. Then, ask yourself, is this the best way of achieving a solution to that problem?