#4 Bayern need to be more clinical
They may have won the game by a solid margin, and they certainly never looked like losing at any point, but the Bavarians did not do so well in front of goal. Scoring three goals in a game sounds great. Scoring three goals from 33 shots isn't the greatest conversion rate though.
Arguably, they hit the bar twice during the match, but howlers like Robert Lewandowski's shot that travelled over the bar were a consistent part of the game. Corentin Tolisso had four shots, but only one on target. Philippe Coutinho had six shots but only one on target. Ivan Perisic had five shots with two on target. Lewandowski had the highest number of shots on target (5) but he had to take nine shots.
These inaccuracies will not take Bayern very far, if and when they enter the knockout stages. The Bavarians need to put more focus on being clinical and efficient in the final third.
#3 Red Star Belgrade were lacking in the final third
The Serbian team had only seven shots at Bayern's goal, compared to the Bavarians' 33. In fact, Bayern Munich had more shots on target than Red Star Belgrade had shots in total. However, it is quite notable that Red Star did not cause experienced Bayern goalkeeper Manuel Neuer any trouble. They had zero shots on target, which is quite appalling for a Champions League side.
Three of those shots came from their wingbacks, with Marko Marin offering another two. The striker Milan Pavkov did not take a single shot, give a single important pass, or make a single dribble throughout the time he was on the pitch.
If Red Star Belgrade don't want to end the group placed 4th, they will need to sit up, especially in the final third, and perhaps cause an upset or two in the coming fixtures.