Last week, we performed Beethoven's 4th piano concerto with the great Marc-André Hamelin. The first horn part isn't that difficult except for one little tricky high, soft and exposed passage starting on a high F# going to A and landing on a D. Just 3 notes that can give you quite a hard time!
As always, we didn't spend much time on the concerto; we ran through it once one day before the concert and again in the dress rehearsal. So all together, I had 3 shots at it.
When I need to perform something like this, I always plan what I'll physically and musically do to make it work. In this case, I practiced taking a deep breath before the F# because it is a lot easier to play with full lungs even in piano and I also practiced playing at a comfortable dynamic so I wouldn't play unnecessarily soft which would have made me tense. It's a solo after all.
Once the piece starts in the concert, the human mind can sometimes start spinning around and over think about that little passage. It goes in all directions and you just don't know if you'll hit your notes or not. I find it very useful to keep reminding myself of the things I will do to make it work and focus on that and only that. I made a plan and practiced it so I'll stick to it no matter what. So in the 7 bars of rest before the solo, I kept telling myself: "deep breath, not too soft" and it worked perfectly every time we played it.
There is no plan or trick that will guaranty you a 100% success rate but at least reminding yourself of what and how you should play before a difficult solo is much better than thinking: " am I gonna make it?...." It makes you more confident too. Like I said already, you need to focus on the means to get there rather than the end result.
At the end, if it doesn't work, at least you can tell yourself that you did everything you had to do and it was just bad luck. Can't win them all!
My guess is that if it works most of the time in your practice room, you have a very good chance of success if you do exactly the same things in the concert. Be aware of what you do, repeat it many times and you'll have something to focus on when that passage comes in the concert.
I am associate principal horn of the Singapore Symphony Orchestra and the author of the progressive methods. I'm happy to share my experience as a horn player and teacher with you.