Put your best foot forward
Embark on a journey or task with purpose and gusto.
This phrase is first recorded in the second edition of Sir Thomas Overbury's poem A Wife, circa 1613:
"Hee is still setting the best foot forward."
The Random House Dictionary of Popular Proverbs and Sayings dates "Always put your best foot forward" to 1495, but provides no supporting evidence for that.
'Put your best foot forward' is rather an odd saying for us to use as it implies three or more feet. When I was at university studying maths, a lecturer worked out the answer to a student's question as 'two quarters'. He then corrected himself and said "we have a special name for that". Likewise, 'the best' is the name we give for something that surpasses all others. Something that surpasses one other is specifically called 'the better', as in one's wife being called 'one's better half'.
Cows (and Rolf Harris) may be able to put their best foot forward but 'better foot forward' makes more sense for humans.
Shakespeare, not usually a stickler for linguistic exactitude, used a 'proper' form of the expression in King John, 1595 :
"Nay, but make haste; the better foot before."
See other phrases and sayings from Shakespeare.
See also: the List of Proverbs.