Staying positive is a deliberate choice; you must make the decision you will stay positive and with it a mindset and a commitment to stay that way no matter what transpires.
Being positive means staying optimistic. If you desire to stay positive, these are words you must erase from your vocabulary.
IF
How often have you heard the limiting word "if" used when someone convinces themselves they cannot rise to the occasion to take on whatever challenges facing them. Even though "if" is used often, do not allow it to creep into your lexicon to mean regret. You will not remain positive when you worry about something you should have done. "I could have won the contest if it had not been for ...." Or, "I could have won the lotto if I had ....." Go forward and do not look back to the "ifs."
I CAN'T
When you proclaim you cannot do something you are setting yourself up for defeat. You can do anything you set your mind to when you are vested in making it happen. Rather than say "I can't," develop a vision and see yourself doing what you consider you cannot do. For example, if you believe you could never become a great cook. Imagine you are in the kitchen with Rachel Ray or Julia Childs. What is unique about them? It should not be your goal to become them, you want to become a great cook and have your own style, but they can help in motivating you and taking you out of the "I can never do that" mindset.
THAT'S IMPOSSIBLE
Nothing is impossible when you are determine. There was a time folks thought it was impossible to walk on the moon, but it happened because there were forward thinking folks who believed nothing was impossible. Start today making the impossible, possible in your life and see how happy and positive you will become.
I'M TERRIBLE AT THAT
You are only terrible at doing something because you have convinced yourself you are. Rather than articulate how terrible you are at whatever challenge is before you, jump right in there and give it a try. So what if you are not successful a few times, keep at it until you master it. You will feel great about yourself and will be open to even greater challenges.
You have the ability to transform your life and make it positive by being mindful of your speech. You are where you are in life as a result of your choice of words. If you believe you are in a rut, change your vocabulary and you will change your life. Get rid of all the negative verbiage. That is the only way you will become and remain positive through the good and the bad.