When to use possessive pronouns vs. dative pronoun + definite article?

Answer 1

The dative pronoun + definite article construct occurs with reflexive verbs,

Here are a two example sentences with the reflexive verb s. waschen

1. Ich wasche mich.
2. here the accusative pronoun "mich" is used because there is no direct object: "I wash myself/I wash up"
3. Ich wasche mir die Hände.
4. here the dative pronoun "mir" is used because the sentence includes a direct object (die Hände): "I wash my hands", or literally "I wash myself the hands".

In short, the possessive adjective will be used when it is used in English except for with reflexive verbs with direct objects