The Blaugrana are unbeaten since a loss to Athletic Bilbao at San Mames at the start of December last year and are currently joint top as they look to defend their Liga crown.
Iniesta, who made his comeback after a four-match absence during Wednesday's 5-1 second-leg triumph, believes his side still must work hard in the coming weeks.
"There will be difficult moments," he told the club's official website. "We have to take advantage of the fact that we're playing well. The hardest - and best - part of the season is yet to come."
Reflecting on his return, Iniesta revealed that he only played 45 minutes due to a pre-match agreement with coach Gerardo Martino.
"I felt good, my impression is that things are going well," he said. "We had already agreed to the substitution. You always have to temper your return and that’s what we did. I feel just as I did before, it’s about adding to the team."