Do what you can, with what you’ve got, where you are.

Theodore Roosevelt (1858–1919) American politician, statesman, conservationist, writer, US President (1901–1909)

Autobiography, ch. 9 “Outdoors and Indoors” (1913)
    (Source)

Variants:

• "Do what you can where you are with what you've got."
• "Do what you can, with what you have, where you are."

Roosevelt in turn labels it as "a bit of homely philosophy, quoted by Squire Bill Widener, of Widener's Valley, Virginia, which sums up one's duty in life," but the quote is usually attributed to Roosevelt.