Manchester City is making preparations to make sure that their performance looks as good as it did this season, but I don't believe that will be the case again because Manchester United, Arsenal, and Chelsea are all planning to play well next season, and even Chelsea, whose performance was subpar this year. The premier league will be very difficult because of how these clubs are switching between teams to sign new players right now, which indicates that it will be a very difficult challenge.
Whatever they are doing for next season, Manchester City need merely keep in mind that there will be a challenge.
Every club is preparing to perform well next season and not only the clubs which you mentioned, dont be surprise if you see clubs that didn't perform well last season performing well next season, from the way things are going, no club should be underestimated. But i still have confidence that Manchester city is going to perform well next season, pep Guardiola is a experienced coach and he is doing everything possible to keep Manchester city in line.
I dont really know how Chelsea's performance will be next season, getting a new coach and players, it wont really be easy for them, so currently i cant predict how their performance will be, but lets just hope they perform better next season.