1. Form and meaning
Many verbs require a particular preposition and case. Learn them as a chunk: warten auf + accusative, sich interessieren für + accusative, teilnehmen an + dative. Use wo(r)- forms to ask about things and da(r)- forms to refer back to things; for people, use the preposition plus wen/wem.
When you study this pattern, identify its communicative purpose first. Then check the verb form, case and word order. German clauses are easier to control when you learn the connector together with the sentence pattern it requires.