The former Barcelona team-mates will meet as managers for the first time on Saturday as City host the Toffees seeking a response to their 2-0 defeat at Tottenham before the international break.
City's slick passing was heavily disrupted by Mauricio Pochettino's side, and Koeman hinted he will employ similar high-octane tactics this weekend.
He told a pre-match media conference: "We are really strong friends and now it's a little more easy because he lives in Manchester and I live close. Sometimes we have time to have dinner.
"He was really interested in the way how we play football in Holland.
"I see a lot in the teams managed by Pep about Barcelona, Dutch football, I like that because that's the most difficult way to win, to play offensive football, sometimes risky, and to win titles.
"Most of the other managers win titles, but not in that football."
Koeman added: "I watched City against Gladbach and it's a very good job to see the difference between how they play this season and how they play last season.
"That's difficult to defend but we have examples of other teams who have gotten results against them."