first: Say the “first two” rather than the “two first,” for unless they be bracketed equal there can not be two firsts. For a similar reason the expression seen in cars, “Smoking on the four rear seats,” is equally incorrect. There can not be four rear (or last) seats; but there can be “the last four seats.” As meaning the four seats collectively which are situated at the rear, the phrase has its only justification.
first and firstly: First being an adverbial form is the correct form to use. Firstly has been used by Dickens, De Quincey, and others but in modern usage first is the preferred form.
first-rate is an adjectival not an adverbial expression. One may say correctly, “He is a first-rate walker,” but not that “he walks first-rate.”
fish: When speaking of fish collectively this word represents the plural; speaking of fish severally the plural is formed by the addition of es.
fix: The colloquial use of this noun for a position involving embarrassment or a dilemma or predicament has not the sanction of literary usage. Do not say “I am in a bad fix” say, rather, “... in a bad condition.” As a verb, it is better unused in the sense of set or arrange. As meaning “put into thorough adjustment or repair,” with the word up added, it is sanctioned by popular usage; but the expression is thought inelegant and indefinite. Some more discriminating term is to be preferred. Fix, in the sense of “disable, injure, or kill,” and “fix up” in the sense of “dress elegantly,” are vulgarisms.
flap-doodle: An inelegant term for “pretentious silly talk characterized by an affectation of superior knowledge.” Twaddle is a preferable synonym. Compare [FLUB-DUB].
flash for ostentatious display, as of money, is inelegant. Display is a preferable word.
flew is often misused for fled. Do not say “He flew the city” when you mean that he fled from it.