The current Super Bowl champions were beaten by the Denver Broncos in their opening game of the campaign, but have lost just once since.
Pees told reporters: "We've obviously improved. The biggest thing in the first game was tackling. If you really think back on the plays that Denver broke for big plays, we missed some tackles and gave them some great opportunities.
"When you looked in a couple weeks later in the Houston game, we gave up no big plays because we tackled well. Last game, we picked up a couple really more on leverage issues than tackling issues.
"We've got to do a great job of tackling. Run after catch is always a key thing. And then the biggest thing about this game coming up, just like any game, is going to be big plays. When we haven't given up big plays, we've played extremely well."
The Ravens host the Green Bay Packers on Sunday.