The Quins currently top the standings in the Aviva Premiership, while they also have a LV= Cup semi-final clash with Bath Rugby and a Heineken Cup quarter-final tie against Munster to come.
"These months are vital and where you have to put the hard work in. We have some big games coming up but we have won nothing yet," he told Sky Sports News.
"We are in a good position to still be challenging in three competitions but we can't afford to relax as we are into the business end of the season.
"We have to focus on each game as it comes along starting with trying to avenge our defeat against Exeter in September."
Next up for Harlequins is a league clash against Exeter Chiefs at the weekend.