Here is everything I know about rehearsing

If you are preparing a 10 minute piece and you have…

5 minutes:
• Do the beginning and the ending, and any tempo changes in the middle.

…10 minutes:
• Play the whole thing once through

…20 minutes:
• Play the whole thing twice through

…30 minutes:
• Play it once through
• Go over any trouble spots
• Play it through again

…60 minutes:
• Play it through
• Go back and work on: rhythm/pulse, intonation, dynamics, balance, phrasing/color, basically in that order (although see below). Once one problem is solved – say, a tuning issue – immediately focus your attention on the next level (balance/color/phrasing).
• Play it again (twice if possible)

Other tips:
• Conductors: don’t let any section sit around too long without playing
• Attack whatever problems you hear. Don’t be cute, or overly methodical, just fix what needs fixing.
• Some problems will fix themselves; it takes experience to intuit which those are.
• Don’t stop too much; some problems will not fix themselves until people have time to practice individually.
• Try to balance stopping for detail work with playing through longer passages.
• Conductors: when you’re playing through a long passage, dog-ear the corners of your score when you hear issues arise so you’ll be able to locate them as soon as you stop.
• Take notes right after rehearsal; a lot of niggling details can be fixed by giving a list to the orchestra (dynamic changes, note errors, etc.)
• When it comes to intonation, don’t be afraid to fix things that sound out of tune, even if you don’t know exactly how to tackle them. If you don’t know if something is sharp or flat, just admit it.
• Or take a guess. If you guess wrong, you’ll quickly figure out that the other option was right.
• When it comes to tuning chords, here’s a tried-and-true method: have the people who play the root play their note mf. Then add the 5th of the chord playing mp. Then add the third playing p. Once you’ve got the sonority ringing true, people can go back to their regular dynamics.
• A well-said image, analogy, or story can inspire a whole new level of playing, but these have to be used sparingly.
• Stay positive, but don’t accept unacceptable results.