The Jamaica international opened his goal account in the opening-day draw with Barnsley after starting on the wing, but with strikers Akpo Sodje and Leon Clarke ruled out through injury, Johnson played alongside Marcus Tudgay up front in the midweek Carling Cup win over Rochdale and scored two more.
Johnson told the club's official website: "It's been really good for so far. I just want to keep on scoring goals now. My fitness feels really good. I'm not setting any targets, I just want to go out and do my best and score more goals.
"I like to score goals, but will play anywhere the gaffer asks me to play for the team.
"I think we're playing better this season so far, we are keeping the ball and passing the ball well, so we have to stay focussed now and keep that up."