There are 191 4-letter words starting with F in the ENABLE dictionary — 5% of all 3,903 words at this length. At 4 points, F is worth more than most tiles without being awkward enough to hold back for — it is generally better placed than saved.
The list divides into 8 groups by second letter, the largest being the 34 words with fa. Scanning the right group is faster than reading the whole list, which is why it is broken up below rather than run alphabetically.
If you know more than one letter, this page stops being the fast way to find it. Enter what you have in the unscrambler — the Contains, Starts with and Ends with filters combine, and setting both length fields to 4 narrows this list to the handful your letters actually allow.
All 191 words, by second letter
FA… (34)
face fact fade fado fads fags fail fain fair fake fall falx fame fane fang fano fans fard fare farl farm faro fart fash fast fate fats faun faux fava fave fawn fays faze
fiar fiat fibs fice fico fido fids fief fife figs fila file fill film filo fils find fine fink fino fins fire firm firn firs fisc fish fist fits five fixt fizz
foal foam fobs foci foes fogs fogy fohn foil foin fold folk fond fons font food fool foot fops fora forb ford fore fork form fort foss foul four fowl foxy foys fozy