The manager is craving consistency as his Millwall side navigate the 'most difficult month' of their Sky Bet Championship campaign.
The Lions have recorded four points from a possible six, beating Sheffield United and drawing away to Aston Villa in an impressive return to form after a luckless November.
"We felt like we left some points on the pitch last month, that's for sure," Neil Harris told millwallfc.co.uk
"However, we have had a positive start to December. It's a tough month, probably the toughest month on paper that we have this season, but we have had a strong start.
"Middlesbrough at home is another tough one. Boro are a team that should be near the top of the League and have spent wisely, recruiting from this level and above.
"Maybe they have been a bit inconsistent but they have really good footballers and have a lot of pace in their team on the counter-attack.
"What a great Christmas period. We have no fear at all and we have to go and attack the games."
The Lions' next three matches are against top eight teams, with fixtures against Middlesbrough, Derby and the League-leading Wolves compounding a taxing run of games.
"You have to give a level of respect to some players," Harris added.
"We will have to be aggressive in our approach but we have to have a patient side too or these teams can hurt you.
"But we to impose ourselves on the game as well. It's not about letting Boro and Wolves dictate play, we have to get about and impose ourselves on the match. That will be key."
Midfielder Shaun Williams will be available for selection after playing extended minutes for the U23s as he continues his comeback from a knee injury.
Goalkeeper Jordan Archer will also be available after recovering from illness, while the match will come too soon for midfielder Fred Onyedinma, Shane Ferguson and Byron Webster.