Avoid dishonest situations

Commit honesty to yourself.
Promise yourself that you will stay honest, no matter what. You can also make a contract for yourself and sign it. But reminding yourself of honesty alone can make a difference.

Recognize your tendency to bend reality.
Recognize the situations where your personal financial benefit stands in opposition to your moral standards. In these cases, you might be tempted to "bend" reality, see the world in terms compatible with your selfish interest, and become dishonest.