We use reflexive verbs when the subject and object of a verb are the same. This means, the subject carries out an action for itself and not for someone else.
True Reflexive Verbs
Rule 1: Some verbs are always reflexive, which means, we can’t use them without a reflexive pronoun (mich/mir, dich/dir sich, ...). The infinitive of these reflexive verbs is preceded by the pronoun "sich":
Rule 2: Reflexive verbs can be reflexive in the accusative or in the dative, but most of the time, we use a reflexive pronoun in the accusative case.
Partial Reflexive Verbs
Rule 3: Some verbs are not always reflexive, we call them partial reflexive verbs. They can be used in both a reflexive or non-reflexive way, depending on the situation. The subject can either act upon itself (aka reflexive pronoun needed) or someone/something else (no reflexive pronoun):
Rule 4: Some verbs can have a completely different meaning when they are used as a reflexive verb.