Learn French: C'est mon dictionnaire, tu me le rends demain, d'accord ? - It is my dictionary, you are giving it back to me tomorrow, right?

In French statements, 1st and 2nd person object pronouns (me, te, nous, vous) always come before 3rd person direct object pronouns (le, la, les). Because me is 1st person and le is 3rd person, the correct order is me le.

Why do both pronouns go before the verb rends?

In declarative sentences (statements), object pronouns are placed immediately before the conjugated verb. Even though English puts them after the verb ('giving it back to me'), French structures it as 'you to-me it give back' (tu me le rends).

Why is the present tense rends used if the action is happening demain (tomorrow)?

Just like in English ('you are giving it back tomorrow'), the French present tense can describe a planned future action, especially when there is a time marker like demain. Using the present tense here also makes it sound like a firm expectation rather than just a future possibility.

Why use rendre instead of retourner for 'to return'?

When you are giving a borrowed object back to its owner, you must use rendre. The verb retourner is mostly used for returning to a physical place, or for physically turning an object upside down.