HSV have endured an inconsistent campaign to date and sit ninth in the Bundesliga table ahead of the weekend, while BVB are 12 points adrift of leaders Bayern Munich.
"Dortmund are favourites. We need to be wide awake from the first minute. Our goal must be to win there," Jansen told Bild.
"We still lack consistency and lose our concentration too much. We're brave but not toxic enough. We hide too much. It is a mystery that I don’t understand."
The full-back has fallen out of favour with Germany since winning his first cap in September 2010, but aims to play his way back in Joachim Low's plans.
He added: "I know that Low looks at the left-back position, [so] I think the cards will be reshuffled soon. Through good performances in the Bundesliga I’ll try to get another chance with the DFB.
"I know that I am more focused. This is my claim, my ambition, my goal. But I am relaxed. When it comes to my performance, I'll be back."