Barca were the team to beat again last season as they swept to another La Liga title as well as the UEFA Champions League trophy.
Iniesta, who made a starring return from injury in Saturday's 3-0 win over Racing Santander, said he was happy with the way things were going this season, but it was crucial for the team to always look to improve.
He told El Marcador on Barca TV that "every year it gets harder to be better than the rest ... it is important for the team to take this as a challenge, to always want to better ourselves".
Iniesta added that "doing what we did last year doesn't mean we can assume we'll achieve the same this time ... the team must never stop learning and improving", especially because "other teams do things differently when they play us".
The midfielder outlined a second challenge for his team-mates which is "to look for different ways of playing in order to counter the things our opponents do".
"When you go out onto the pitch you always give 100 per cent, and it is very hard to think about reserving yourself. That isn't my way of thinking, and neither is the way my team mates think," he said.
Barca have now gone 12 games unbeaten in all competitions following Saturday's game with Racing.