The dictionary aggregator Logeion is the go-to place for this - on the right it not only shows the word's frequency but its most common collocations as well. The spelling VAS for instance represents two different lemmas - vas 'a human bail' & vas2 'a vessel', and Logeion gives separate collocations for each of them, one under the other; however, only vas2 is given frequency information (hopefully this will be improved upon).
Generally you can judge the frequency of a word by the number of citations in L&S and the relative length of its entry - although sometimes they just give a list of citations while barely quoting any, as with doctor.
In the Frequency section you can click on the names of authors to see all occurrences. Sometimes it will search for the wrong of the two lemmas - for example Tibullus never had the occasion to use the word ānus 'butt-ring'. To search for the other lemma, anus 'old woman, gramma', change 'word=lemma:anus' for 'word=lemma:anus2' to get the following list.
Apart from that, the basic way to check word frequency is searching a corpus, usually PHI - but if the word has homographs (which most Latin words do), it's up to you to “lemmatise” it.