Those of us who've performed a lot tend to cultivate routines for how we like the day of the concert to unfold. We develop a preferred set of activities and behaviors that come to be meaningful as we prepare ourselves for performance. These can range from sleeping patterns to food to practice schedules to warm up routines and more, and our dedication to them can be intense.
When you are starting out, it won't be obvious what is best for you. Do you need a long and high-quality night's sleep or will it not really matter? Does the food you eat impact the quality of your performance and if so, how? Should you drink coffee, wine, etc. that day? Do you need to practice that day and if so how much, and when? When, relative to the day of the performance do you like to replace your strings? How much before the concert do you like to be at the concert location? How much stage-time do you need before you go on? When do you like to dress?
Artists who perform regularly tend to know the answer to these and similar questions. Everyone, though, is different. In my case, I've been fairly deliberate in avoiding attachments to specific routines, though I have preferences. The reason is simple: you can't always control events and I prefer to remain unflappable. Of course this is a bit of an artificial construct: I teeter close to the edge of obsession over certain elements of the routine but quite deliberately convince myself that they don't matter.
The amount you perform is a huge determinant in this discussion. Players who truly and regularly "tour" more readily become inured to these issues. They can play the program and they know it, and they understand that it doesn't matter that much about the rest of it. Still, others become even more religious about their specific routines thanks to the repeated opportunity to test and refine them.
It is hard to offer prescriptions for what is best beyond the general, as everyone is so different, but I'll offer thoughts on some of the items listed above and indicate my own preference as a reference point.
I've found food matters some. It's a bad idea to make two hours before you play the first time you ever try a strong and unfamiliar dish (like a curry)--your stomach may prove a distraction as you try to play. Similarly, caffeine should be kept to normal levels-neither more nor less than usual. Most people find they prefer to eat after playing, not before, but you can overdo the notion and find yourself feeling hungry and under-fueled. I like to eat something light a couple of hours before when possible.
Practicing routines will vary widely. I like to visit with every piece on the program during the early part of the day and then leave the instrument alone until pre-concert warm-up, but I've known many who play the guitar all day before a concert. If I play all day, I'll feel fatigued and my bass strings will lose much of their freshness. I feel that if the material is not ready by the day you have to play it, practicing madly in the hours immediately before the show is unlikely to help.
It is sensible to plan on arriving at the venue at least 90 minutes early. I always go dressed. The main reason for this is simple convenience: it's generally more comfortable to dress at the hotel or house where you are staying than at a concert venue, and carrying clothes around seems like an invitation for problems (where are my shoes??!)
One of my least favorite moments is the dead time between the on-stage warm up and the start of the show. This is the time when, if I will feel nervous that night, the nerves begin to accumulate. My normal strategy is to make sure there isn't enough time for this to happen. That is, I try and time it so there is a very short stretch of backstage pre-show pacing in circles. This may be unusual as presenters are often surprised I don't want more time at the hall. But that's what works for me.
Instead, I prefer to spend time walking outside in the afternoon at some point, thinking-through the program, visualizing playing the music, getting centered. Also, that is the best time, for me, to mentally rehearse what I might say from the stage. Once you've arrived at the venue, quiet time is hard to come by. There are the hosts and the venue personnel, from sound people to stage managers to ushers. There is sometimes little opportunity to isolate yourself from the public until moments before curtain time. So I've found the less time there, the better! Others will disagree. The key is to pay attention to what works for you. As you perform more and more, you'll see patterns of cause and effect: practice all day = too tired during concert; arrive too early = too many distractions to feel centered at the concert's outset; eat huge lasagna dinner right beforehand = feel groggy and unfocused while playing. In the end, you'll have a clear sense of what works best.
But as I mentioned earlier, it is helpful to try and avoid too "religious" an attachment to the routine. Circumstances will always be unique and you will often have little control over them. Keeping an open, cool-headed attitude on concert-day can be very helpful in avoiding feeling stressed. And the more you play, the easier it gets.