Mentors of Mussar teach us that Teshuva does not mean to be better. It means to be different. The fellow who discovers that he got on the train that is going in the opposite direction from his destination cannot just get up and sit in the seat facing the direction of where he wishes he was going. He's got to get off the train. Find where he went wrong. And start on a new track. When people discover that they have gotten themselves into a habit that does them no good, the solution is never on the same plateau as the problem. Only uprooting and starting again can make the difference.
This we find in the words of Rabbeinu Yonah in his Iggeret Hateshuva. There is only one way to do Teshuva: It is by seeing yourself as a new person and starting afresh. Getting into the "now" and making sure that you do your best that such a mistake will not be repeated. It is not to live in the past and in regret. Regret is a delicately sensitive feeling, and one that has its very specific time and place. Regret can be effective only AFTER a person has changed. Despite the fact that Teshuva is a combination of חרטה and קבלה על העתיד , Regret for the past and Accepting a new path for the future, Teshuva does not start with regret. (This may be the reason why G-d made Rosh Hashana before Yom Kippur: to teach us that before we work on atonement, scrubbing the sins of the past by means of regret, we must initiate a new beginning.) And most people get so busy with regret that they just never do teshuva, no matter how much they try.
Imagine someone who speaks gossip about his/her brother only a day after Rosh Hashana. He wishes he had not said what he did. He feels so bad about what he said. For some people, this feeling stays for a few minutes, and for others, a few days. But most people get so engrossed in the thought of the past, so involved in the regret, that they just forget about what they should do to make sure that they won't ever speak about their brother like that again. Real teshuva would be taking fifteen minutes a day to study Shemirat Halashon.
This is true about most things that we would like to do teshuva for. We usually attempt teshuva on things that we feel bad about. And then, we get so busy feeling bad about them that we get sidetracked and end up not rectifying them. Regret, says R' Yonah, should be reserved for after change. When someone recognizes faulty behavior in himself, he should first figure out what new habits need to be adopted. Then, he should put the new behavior into practice, and only then, after he has already affected a change, can he go through the hell of regret.