How do I know whether a verb takes 'à' or 'de' as a preposition?

Unfortunately, like with many things in French, the prepostition that a verb or phrase takes is something you just have to learn by heart!

Fortunately, below I have made a list of the verbs and prepositions that you will most likely encounter/ need to use on a regular basis!

À

aider à - to help to…

apprendre à - to learn to…

arriver à (faire quelque chose) - to manage to (do something)…

commencer à - to begin/to start to…

continuer à - to continue to…

s’habituer à - to get used to…

réussir à - to succeed at…

De

avoir besoin de - to need…

choisir de - to choose to…

conseiller de - to advise to…

décider de - to decide to…

essayer de - to try to…

oublier de - to forget to… 

parler de - to talk/speak about…

refuser de - to refuse to…

If you remember all of these, it should help you a lot in your studies, as they are commonly used!

If you would like help putting them into sentences or would like to learn some more, please arrange a tutorial!