There are no grammar rules to guide you regarding "too", "as well" and "also". "Too" can get confusing because we also have "to" and "two", so in conversations "too" is informal and most often comes at the end. "As well" is more formal and comes at the beginning, in the middle ("as well as") or at the end ("as well"). "Also" is from the original English and has a meaning of "in addition to" or "besides", so "also" is something a little more in meaning.