The Cobblers sit only two points above basement side Torquay in 23rd place ahead of Saturday's trip to fellow strugglers Bury.
Northampton go into the game in improved form and Boothroyd is hopeful they can continue that into the busy festive period.
"December could be a season-defining month for us, and it's important that we don't dwell on defeats and that we quickly focus on the here and now," he told the club's official website.
"We've picked up seven points out of 12 in our last four league games so there has certainly been an upturn.
"But we've got to maintain that and keep that going in what is going to be a massive month for us."
Boothroyd added: "If we can keep everybody fit, then I'm absolutely convinced that we are heading for a happier second half of the season."