Fleck, speaking after his team's come-from-behind 40-34 win over the Cheetahs at the weekend, said they gained a lot from the trip to Bloemfontein.
"Obviously a big work-on for us is discipline," Fleck said, adding: "That is what allowed the Cheetahs back into the game."
The Stormers had two healthy leads - 26-10 and 33-20 - before going behind and required a 73rd-minute Sikhumbuzo Notshe try to save the day.
"That is something we have to look at," Fleck said of his team's poor disciplinary record.
The win over the Cheetahs included a red card and two yellow cards to go with the 11 penalties.
They have already conceded two red cards and seven yellow cards this season - with banned loose forward Rynhardt Elstadt one of biggest culprits, contributing a yellow card and red card against the Cheetahs.
Apart from the harsh 'lesson' about his team's discipline, Fleck said the challenge was complacency and not getting things right.
"There's a lot we can take from this game with some of the work-ons being our defence," the coach said.
"I don't think it was 100 percent throughout the game and we let in some soft tries.
"If we want to go further in this competition‚ those are the things we need to sort out.
"There is certain things we can work on before next week's game [against the Sunwolves] and the quarterfinal.
"We are looking forward to the Sunwolves game,"
The Stormers will get some players back from injury - like Springboks Damian de Allende, Eben Etzebeth and Siyamthanda Kolisi.
However, fullback Sarel Marais is in doubt after he hyper-extended his knee against the Cheetahs.
He will go for scan and Fleck said "hopefully" it is not too bad.
Fleck also revealed that he will be using Under-20 star Damian Willemse as a flyhalf only.
Willemse was used as an inside centre in the World Rugby Under-20 Championships.
"We see him as a flyhalf and that's where he played at school level‚" Fleck said.
"I know they used him as a centre in the Under-20 team, but he's a No.10 for us.
"He's a young kid with lots of talent and there were some brilliant touches from him.
"There were one or two mistakes but that's to be expected from him because he's young. For him to performance at this level was a big ask away from home and he's delivered."