Samba Diakite, Ryan Nelsen, Andy Johnson and Robert Green have helped to bolster the Loftus Road ranks.
"Getting business done early was always the aim," he told the club's official website.
"As soon as the season finished I was scouring Europe, going to France, Germany and Spain all in the space of six days, to look at players, with a view to getting business done early and getting in front of our rivals and setting a marker in terms of what we're trying to do here.
"Hopefully the early work we've done will reap benefits in the future.
"If we can get everyone through the door that we want then we'll be absolutely delighted."