"If there is anything I really need to work on is getting that fastball down," Cishek said on Monday afternoon.
Earlier in the day, Cishek had a discussion with manager Mike Redmond about executing better.
"I had a good talk with Red earlier, and I'm just going to keep battling and doing what I do best," Cishek said.
It's been a rocky start to the season for the Marlins, and Cishek has also had his moments. On Sunday, he closed out the ninth inning for his second save in a 6-4 win over the Cubs. But in the ninth, Dioner Navarro homered.
In the first game of the series with Chicago, on Thursday, Luis Valbuena homered off Cishek in the ninth inning, delivering the game-winning hit.
"The mistakes, I'm just not getting away with them right now," the right-hander said. "That's part of the game. It's the ninth inning, everyone is dialed in. I'm learning that part also. Keeping the ball down is what I'm mostly trying to focus on."
Cishek entered the series with the Mets posting a 1-3 record with a 5.73 ERA, allowing eight runs (seven earned) in 11 innings with 11 strikeouts.
In 2012, Cishek was the Marlins' top reliever, and he enjoyed a strong April, going 2-0 with a 0.96 ERA with nine strikeouts in 9 1/3 innings.
The most encouraging news for Cishek on Sunday was the effectiveness of his slider.
"I feel like I'm throwing the ball really well," he said. "I just made a couple of mistakes that got hit out of the park. I'm not getting away with those mistakes pitches. Mentally, everything feels really good.
"I had a good feel for my slider [Sunday], for really the first time this year. I'm just going to build off it."