Work through pieces slowly.
I decide on my time frame for a concert preparation depending on the program. l always schedule more time than I think I really need, just to be safe. I have specific goals in every piece so I can keep those in my mind when prioritizing practice hours.
In the beginning I work through pieces slowly, spending as much time as I need on any section.
I might spend a whole practice day on just one passage in a piece. Once I start getting specific sections under my fingers, I start working on more repertoire in one practice session. I will be spending less and less time on the challenging sections as my performance preparation progresses.
As time goes I start to realize which particular spots need more work or maybe less work than I expected. My preparation plan is always changing depending on how much time I have and what needs the most work.
I try to have everything musically planned and technically prepared at least a week before a recital. That gives me an opportunity to focus more on fundamentals and playing the hard technical passages daily.
This process helps me maintaining my confidence. I try to play few mock recitals to check things like endurance and musical pacing. Ideally I record a run through at least once before the performance. It creates a feeling of a real performance and provides an opportunity to study my performance
I try to take as easy as possible the day before a performance. Getting a good night sleep before a performance is very important .
In the day of the performance I do a good warmup few hours before the time to play. I want to be warmed up but not tired. I do my regular warmup routine and maybe run some technical passages slowly, just for confidence. I stop before getting tired even if I feel like I want to practice more.
I eat a good meal around two hours before a performance so I have time to digest the food but not feeling hungry again. If I have time, I do stretches to make sure everything in my fingers, arms, and breathing muscles is working smoothly.
Finally I do a very short version of my earlier warmup around half an hour before the performance to check things one last time. At this moment I accept that I have prepared as much as possible and focus on my musical goals and enjoying the performance.