By rule of thumb: to do any thing by dint of practice. To kiss one’s thumb instead of the book; a vulgar expedient to avoid perjury in taking a false oath.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Thrums * ThcmmikinsNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes