Start making a conscious effort to choose your words carefully before you speak. Say kind words. When speaking to others, squelch any words that convey critical thoughts or judgments.
Offering constructive criticism to someone has its place. Only give it whenever it is requested or if it is truly required, such as when a parent is teaching a child, or an employer needs an employee to meet certain job requirements. Remember: Unasked for advice is really a form of criticism, so be careful when you offer advice.
In most circumstances, criticism is regarded as a “put down” that hurts both the criticizer as well as the target of the criticism. You don’t want to be on either end of those hurtful words.