Samoa went down 20-10 in Ireland last weekend. But Ireland's win was far less convincing than the result suggests and the physical Samoans pose a real threat at Twickenham.
"The trick against Samoa is that we take care of our performance and mindset," said Johnson.
"We have to go out there and get the tempo like like we did last week. It is about keeping the foot down.
"The key is having the right mindset. That is what good teams do - go out and play. That is what we are trying to do, become consistent.
"We need to try to be better this week. Samoa are a real, real danger this weekend. This is no different to any other Test in the series. They have our full attention.
"They are a very dangerous side. They could have beaten Ireland last week.
"They have a very solid and competent set-piece, they are very comfortable on the ball. Samoa probably edged the breakdown against Ireland.