Celtic made a slow start to the new campaign, but they are unbeaten in their last six matches.
The Bhoys dropped out of the Champions League and fell behind Aberdeen in the Scottish Premiership standings over the early months of the new term, but Deila coped with the pressure well.
Armstrong says that the Norwegian manager knows when to shout at his squad, and when a more measured approach would be the better option.
"The manager has his ways," Armstrong explained. "He’s well balanced. He knows when to be calm and when to speak to us in a certain manner when it is required.
“But we have an experienced group and the dressing room knows the situation."
Celtic's poor start to the new season was a disappointment, but they do appear to be starting to click into gear now.
The Bhoys are unbeaten in their last six games, and they have closed the gap at the top of the Scottish top-flight to just one point.
Deila's side have also made a decent start to their Europa League campaign, and picked up credible points against Ajax and Fenerbahce.
It gives the side plenty to build on when they return from the international break, with their next game coming against Motherwell in two weeks' time.