лучше бы ты делом занялся.
I kind of know what each of these words mean individually but I am discovering that knowing the dictionary definitions of words in a sentence is really only the tip of the iceberg when it comes to translating said sentence. The thing is more than merely the sum of its parts. делом is so broad a word that I'm not sure which of it's meanings is relevant here and I do not know why it is in the prepositional case. I feel as though the sentence means something like "You had better do the thing" or "You'd better do that" Any one who can shine some light on this would be appreciated. Thanks.