There are various ways in which the phrase "behave better" can be rephrased, depending on the context in which it is used. One way to express the same idea is to say "improve behavior", which implies that there needs to be a change in the way a person is acting. Another way to convey the same message is to use a more specific phrase, such as "act more appropriately" or "display better manners". Similarly, "conduct oneself more positively" or "be more respectful" can also be used to convey the same sentiment. Ultimately, the specific phrasing used depends on the situation and intended audience, but all of these phrases convey the idea of needing to behave in a better or more desirable way.