In dealing with others, the best rule is to start from a place of trust, realizing and accepting that you could be wrong. People tend to respond to you in the same way you act. You will receive far more trust if you offer trust. If you offer distrust; that is what you will usually get back.
In dealing with problems that need positive responses, we are more effective (and feel better) being assertive instead of aggressive. When we respond from our thinking, we choose a thought out response rather than an emotional one. We can be assertive and accomplish what we feel we must, without being angry. It is much easier to be assertive rather than aggressive if we have not set up some expectations that upset us when they are not met.
We need to learn to not let our peace of mind become dependent on what another person does. Except for adhering to the laws set down by our society, we have no right to expect that anyone act in a certain way, just as they have no right to require that from us.