Schalke have been struggling this season since their promotion after a year in the second division but four consecutive goalless draws and two wins has moved them off the bottom spot.
"We are really happy with what we did in the past weeks," Schalke forward Sebastian Polter (31) told an international media round table on Friday. "The turnaround is not easy but we did it.
"The last six games we concentrated on defending well and start from there. This is the basis to stop conceding goals all the time."
While Schalke have managed to plug the holes in their leaking defence, they are still struggling up front with only 18 goals in 23 matches and just four in the last six games.
With Dortmund on a perfect eight league game winning run in 2023 Schalke will need to up their scoring rate if they are to get anything out of the derby.
"We know we have to score goals and improve our attack," said the forward who joined Schalke this season.
"Sometimes one goal is enough if we keep a clean sheet."
Dortmund are currently in second place on goal difference, level on 49 points with leaders Bayern Munich. Schalke's 2-0 win at Bochum on Saturday lifted them into 17th place, level with 16th-placed Hoffenheim and Stuttgart in 15th on 19 points.
"Our confidence has been growing in the past weeks. You could see it week by week," said Schalke keeper Michael Langer.
"Dortmund are playing for top spot and we are fighting downstairs for points. But now we are in good shape and have good confidence for tomorrow."
For his teammate Polter, who has played for a string of Bundesliga clubs, battling to avoid relegation is not new to him, having done it with Bochum last season.
"I had this quite a few times at other clubs. It is something I know," Polter said ahead of the biggest rivalry in German football.
"The derby is important for the city, for the members of the club. We players have to put our heart on the pitch. We want to give them something back. They have suffered not only the last couple of years but also this season.
"We did the turnaround but we want to give something back," Polter said.
