They say language is an ocean which can never be learnt completely or fully in that I would say grammar plays the most important role than vocabulary of words because even though you’re well versed with millions of words if you cannot weave it beautiful grammar it all goes in the vain, you’re as good as an illiterate. Hence always get your grammar right even before the words maybe, start with something like parts of speech.
Tip time! Adverb is something which describes an action and an adjective is something which describes a noun.