Dortmund finished second in the Bundesliga last term, trailing dominant Bayern Munich by 19 points come the end of the campaign.
However, Klopp's men picked up two wins from four against Bayern in all competitions last season, with the eight-time German champions strengthening their squad in recent weeks.
Ciro Immobile, Adrian Ramos and Ji Dong-won have all arrived to help fill the void left by talisman Robert Lewandowski - now at Bayern - but Klopp is eager to focus on defensive improvements.
"We should focus next season to concede fewer goals. We played great [last season], but there's still plenty of room [for improvement]," he told Bild.
"In the direct games against Bayern, we were not 19 points worse.
"But we have not been able to play as constantly as Bayern."
Klopp could welcome back a number of FIFA World Cup winners into his defence ahead of next season, with Germany's Mats Hummels set to feature in the final against Argentina on Sunday.
Goalkeeper Roman Weidenfeller is also in Brazil alongside Marcel Schmelzer, Erik Durm and Kevin Grosskreutz.
