How should one behave while projecting?

It really depends on how objective the Astral dimension is. If you think that dreams, OBEs, so-called "Astral Projections" are all but a figment of your imagination, and that such things do not have any subjective reality, then there is no specific rules of behaviour, except those designed to help you retain control of the experience and to prevent any distressing experience.

On the other hand, if you believe that there is some degree of objective reality to the dimensions beyond those of our physical reality, then it means that individuals and entities you might meet there also have an objective existence independent from your own. In such a case, don't behave there in ways you wouldn't behave here. Don't do to people there things you wouldn't do to people here. The same rules of common courtesy apply in every dimension.