Be mindful of the opinions that you let in (this includes other people’s opinions, but also your own).
Don’t keep naysayers or pessimists around. Their attitudes and opinions will rub off on you if you let them. Instead, surround yourself with positive thinkers and doers. If you have trouble finding these people, look to books to aid in your pursuit. Read about Teddy Roosevelt, Marcus Aurelius, and Jesus. Read Dale Carnegie, Stephen Covey, and Jim Collins. Learn about innovators such as Thomas Edison, Nikola Tesla, and even Albert Einstein. Imagine learning lessons from history’s most influential minds and how they can positively impact your life.
Don’t forget to also be careful of what you tell yourself, whether it is positive self talk or negative. Remember, when things are going well, you’re never as good as you think you are, just as when things are going poorly you are never as bad as you think you are. There is always some element of luck involved in the result. It’s your job to control what you are able to control and let go of the rest.