This is a complex question requiring a complex answer, because it all depends on what kind of language you examine. Corpus evidence used in the ‘Longman Grammar of Spoken and Written English’ shows the following approximate frequencies of thousands of words per million:
Primary auxiliary verbs 85
Adverbial particles 10
Primary auxiliary verbs 65
Adverbial particles 5
These figures can give only a crude picture and show only the figures for one kind of written English. In general, though, nouns and verbs are the most common words, and conversation seems to use a higher proportion of verbs, adverbs and pronouns, while written English uses a higher proportion of nouns and adjectives.