The two nations meet at the Millennium Stadium this evening, with both able to win the championship.
The England captain told Sky Sports News: "When you come to a place like Cardiff, you might get one or two chances, and we've got to make sure we are good enough to make it count, whether it is the first minute or the 80th minute.
"It is one thing saying it and it is another thing doing it. That is the challenge we have. Of course, everyone wants to go out there and win, but it is about how you go about it and breaking it down into the smaller, finer detail.
"We can't afford to switch off at all or lose concentration or lose our composure. If we get a chance in the first or 80th minute we need to be mentally prepared and right up for it."
England will still win the tournament if they lose by less than seven points.