After his double in their Champions League win against Benfica, Barnes admits their finishing hasn't been good enough this season.
Speaking to NUFC TV, he said: "We've sort of been guilty a little bit this year of not going and getting the second and third goal and killing games off. So against Benfica, it was really pleasing to go and do that.
"You obviously have your responsibilities to help the team defensively but, as an attacking player coming on, it's important to go and help the team push on, go and get the next goals. We've probably not quite hit our heights this season of that free-flowing football, scoring, creating chances. That's what we do at our best, that's what we did last season.
"It's something that we know we're not quite there this season, but we're working on it. You see, against Benfica, when it does work, it really does, and we score goals, we create a lot of chances. So it's just about taking that into the next few games."