Use the big thinker's vocabulary. Use big, bright, cheerful words. Use words that promise victory, hope, happiness, pleasure, avoid words that create unpleasant images of failure, defeat, grief.
Remind yourself regularly that you are better than you think you are. Successful people are not superhuman. Success does not require a super-intellect. Nor is there anything mystical about success. And success doesn't based on luck. Successful people are just ordinary folks who have developed belief in themselves and what they do. Never - yes, never - sell yourself short.