A quick entry to remind myself of the importance of the first try in practicing.  The usual practice method is to pick a tough spot, work on it for a while until it gets better, then, satisfied, move on to another spot.  Most often the first pass of the tough spot goes by without a thought, since you have the chance to work on it.  If there is a thought, it goes something like, "wow, that was bad, this needs work".  You knew that before you played it!

The first try should give you an indication of what that spot would sound like in a performance.  Remember that in a performance your nerves are up and not everything comes off at its best.  So, if you're performing a piece tomorrow, and your first try at a certain spot is bad news, it will probably remain so in performance the next day.  That's why advance preparation is so important.  The tenth try, the one that finally satisfies you, is much less relevant.  It points to where your first try might be in a week's time, which is good to know.  But that's a much hazier concept thatn the here and now.

This shouldn't be taken as doom and gloom, though.  The good news is that if you give sufficient time in between, you can have several "first" tries each day.  In fact, this is absolutely essential to speeding up the work process.  Do your first try, but listen objectively with the object of prioritizing the things that need work.  Not just "that was bad", but "the second measure felt shakiest because of the string crossings."  So spend 60 seconds working on that and do another pass or two.  Note any changes that resulted, and move on to do a first try at another spot.  Half an hour later, return to the first spot for a fresh "first try".  Now you're getting performance practice every half hour!