Green’s Dictionary of Slang

to smarten (oneself) up.

1620		T. May Heir II i: See how th’ old ape smugs up his mouldy chaps / To seize the bit?
1623		Middleton & Rowley Spanish Gypsy IV i: Smug up your beetle-brows, none look grimly.
1668		Etherege She Would if She Cou’d III ii: For he that would have a Wench kind, / Ne’re smugs up himself like a Ninny.
1780		T. Gray Candidate 1: When sly Jemmy Twitcher had smugg’d up his face With a lick of court white-wash, and pious grimace, A wooing he went.