that is where experience really comes into play. "ok my usual playstyle of hitting it flat and hard is not working.. it keeps going long or into the net... time to switch it up before the scores to uneven"
you can maybe stick to your usual playstyle and hope it comes together.. hope...
or have a backup plan and start really swinging low to high fast for net clearance and for the ball to stay in the court..
is like when your "in the zone" you can do anything. but you can't always be in the zone.. you gotta be able to find a way to win without relying on yourself being in perfect playing condition.
"i usually can ace all my serves but now i am double faulting constantly"
maybe just focus on setting up the next shot with your serve and not trying to win the point via a serve.
don't want to leave to lengthy of a reply if what i said is not what you're after.
maybe some more experienced posters can share advice