Midfielder Massimo Luongo believes Ipswich must keep doing "the little things right every day" to sustain their bid for back-to-back promotions.
It was their seventh successive victory at home and they are just one point behind Championship leaders Leicester.
"December will highlight which teams are going to push and which aren't," Luongo told BBC Radio Suffolk.
"We're there for a reason, so why not (us)? But our culture as a club isn't why not, it's do the little things right every day, go in every day with the proper attitude - and we'll do that for the next game and then build up for the next game doing the same thing and suddenly, we'll be in February and see where we are, then March.
"That's all we've been doing so far and I think it's working."
Luongo was back in the starting line-up against Millwall, having come off the bench in their two previous games.
He marked his return with a superb strike into the bottom corner to put Ipswich 2-0 up after 12 minutes and was only inches away from another in the second half.
"Most managers do rotation as part of the game. It's just the way the game goes. I was picked today, might not be picked on Saturday. I've just got to get my head down and when I'm called upon, be ready," the Australia international said.
"I don't score many from outside the box but I think that's two this year. I'm finding more areas where I can get in the box or an attacking position, it's not part of the game I base my strengths on but I like to get a goal and it feels good.
"When it's your game, it falls to you all the time. We were pretty unfortunate not to make it four or five but it was a really good performance."
Ipswich - who have only lost twice in the league this season - will play seven games in December, starting on Saturday when Coventry City are the visitors to Suffolk.
They will also be at home on 16 December for the East Anglia derby against Norwich, which will be followed by possibly their two biggest tests of the season so far, a trip to third-placed Leeds United and a Boxing Day showdown with Leicester at Portman Road.
"We're a really good team and we have to all chip in, all be connected and all play a part in every win," Luongo added.
"We're getting to that period where everyone is starting to look and see where we are (in the table) and look at the other scores.
"The gaffer will probably remind us to keep our heads down, stay as humble as we can and take every game as they come."