darauf, worauf and verbs with a fixed preposition

First learn the complete government pattern: warten auf, sich freuen auf, denken an, sprechen über, sich interessieren für, sich kümmern um, bitten um, teilnehmen an. The preposition is not copied automatically from another language; it is learnt with the verb, as gender is learnt with a noun.

In these combinations, government also fixes the case: warten auf takes the accusative even though nobody moves, and teilnehmen an takes the dative. Movement does not decide the case of a fixed verb-preposition pattern.

For neutral pronominal reference to a thing or proposition, use the prepositional adverb: «Ich warte auf den Bus» becomes «Ich warte darauf». An explicit group such as auf das may occur with demonstrative force, but it is not the default neutral pronoun. If the preposition begins with a vowel, r appears —darauf, daran, darüber—; before a consonant it does not —damit, dafür—. With people, keep the preposition separate: «Ich warte auf ihn».

To ask about a thing, use wo(r)-: «Worauf wartest du?», «Womit fährst du?». If an infinitive clause or subordinate clause completes the governed pattern, a da(r)- form can announce it: «Ich freue mich darauf, dich zu sehen».

Formation becomes regular after the lexical government has been learnt. For a thing or proposition, da(r)+preposition refers back and wo(r)+preposition asks; for people, keep the preposition separate with a pronoun or wen/wem.