Here's a goot tip from USA Swimming.
My tip would have just been "Swim Really Fast."
"“Thinking too much can slow tempo down and take focus away from racing,” says Adam Mania, assistant coach at Schroeder YMCA Swim Team in Brown Deer, Wis., and 2004 Olympian. “Muscle memory can develop very quickly, so I promote focusing on perfect swimming in practice. That way when it is time to compete, swimmers can just get up and race.”