How do you translate "Yesterday it rained, however, so I decided to go by bus." ?

I would translate this sentence as "Però, ieri ha piovuto, quindi ho deciso di andare con l'autobus." As you can see, I rearranged the two conjunctions to avoid the sentence sounding too heavy, but this isn't overly important. What matters, and one must truly pay attention to, is the "go by bus" part. With this, there are different ways you can translate it, but they take different prepositions: "ho deciso di prendere l'autobus" "andare con l'autobus" and "andare in macchina". Prepositions are often the trickiest part of learning a language as they often don't directly translate from our own language, therefore, often it is a case of memorising what verb takes what preposition- using flash cards and reading a lot will help with this process.