The pair worked together successfully at Bayern Munich and have now been reunited.
Poland striker Lewandowski said from Barca's US camp: "I am sure that this season I can score more goals than last year, but getting the number of goals right... 23-24 was not good for us or for me in particular, but we are Barça and we have to take a step forward."
It's been suggested Flick's more direct style could also benefit him.
"The more offensive, the more scoring options I will have. We must always seek defensive-offensive vigilance. We cannot attack and not think back.
"Now we have time to understand the direction we want to go. We want to prepare the season very well. You always want to win, go to the final, win a title, but first be clear about what we want to do in the games," added Lewandowski.