Robin van Persie, Shinji Kagawa, Nick Powell and Alexander Buttner are the four new additions to United's squad this season, with Angelo Henriquez expected to complete his move from Universidad de Chile in the coming days.
"When you see top players come through the door, it gives everyone a big lift," Carrick told United's official website.
"It puts everyone in a positive mood because it means the team is moving forward, but you also know you've got to play well to stay in the team and that helps keep the standards high.
"It's up to us to learn the strengths of the new players and for them to fit into our system and I'm sure we'll get better as the season goes on."
United will entertain Fulham at Old Trafford in their second Premier League game of the season on Saturday.