Confident is not a four-letter word. Do not confuse confidence with conceit. Take that as a compliment. Eliminate the words cant, wont, couldnt, wouldnt, shouldnt, will not from your vocabulary please. That is an excellent place to start on the road to positive thinking.
Negations produce similar type feelings within.
They make you feel crappy. Your head is held a bit higher, your heart feels a bit lighter yet stronger, and your posture is more erect. Keep that in mind. Make an effort to go about your day without using negations in your sentences. You can say the same thing as a positive.