Optimist is an antonym of pessimist.
The best way to be optimistic is first to gain an awareness of when you are NOT being optimistic. Know when you are seeing things in a negative light, and change that thought pattern. Second, be aware of what is going on around you, and within that look for the positive things. A pessimist will see the negative in every positive, while an optimist will see the positive within every negative. Constantly be thinking of the positives within every situation. In a way, it is attempting to find the bright side to every situation. Even when there doesn't seem to be a positive, being optimistic is thinking deeper, until you find it. For example: Let's say that you were driving somewhere, and you get into a fender bender... A pessismist would think: "Oh my gosh, I can't believe I just wrecked my car! This is terrible!" An optimist would think deeper into the situation and find the bright side: "Oh my gosh, I just wrecked my car! Well, at least on the bright side nobody was hurt."