Use function instead of match when possible; it'll save 6 characters for 1-character variablesvariable names:
let f=function // ... (14 chars) vs
let f x=match x with // ... (20 chars) It can also replace any pattern match to consistently save 1 character:
match a with| // ... (13 chars) a|>function| // ... (12 chars) (function| (* ... *))a // (12 chars)