Bayern recovered from a slow start and 3-0 loss to Paris Saint-Germain, a result that cost Carlo Ancelotti his job as head coach, to finish second in Group B, level on points with the Ligue 1 heavyweights.
Besiktas, meanwhile, topped Group G, four points clear of Porto, and will be aiming to spring a surprise against the Bundesliga title-holders in the first leg of their round-of-16 tie at Allianz Arena on Tuesday.
"This is always a very special phase," Hummels told a news conference ahead of the visit of the Super Lig champions.
"The nice thing is that it does not necessarily take polish to win. Often, other things are more important than aesthetics.
"We know that we are really meeting a top European team who have convincingly won their group.
"They have big names in the team. They also have, as we have seen on the videos, real quality in their game, tactical and individual.
"That's why we should first deal only with the fact that we [must] beat Besiktas and get us a good starting position in the home game."
Hummels claimed Bayern have made steady improvements under Jupp Heynckes, who was tempted out of retirement to replace Ancelotti following the heavy loss at Parc des Princes in September.
"That's a long time ago," he said of the calamitous showing in the French capital.
"The result was as bad as the game was. We did not have to lose that game 3-0. We know we were capable of better and we made some good progress since then.
"But there is still much to improve if we want to win the Champions League. This can be the next step."