
Jocularity alone is not enough to lead a session successfully, so here are a few other tips that have served me well over hundreds of recording sessions:
1. Raise the height of every music stand before the players arrive: At first glance you may not see the wisdom in this practice. Often musicians are sight reading the music so ideally the conductor and the sheet music should both be in the line of sight of the instrumentalists. However the conductor podium tends to be much higher than floor level and music stands are always placed in their lowest position. So if you don't raise them everyone's face is buried in the stand and not looking your way.
2. Diplomacy: Someone in the 2nd Violin section is consistently out of tune on a particular note, and you know exactly who it is. I don't recommend calling that person out. I will spread the blame a little and say, "2nd Violins, we seem to have a disagreement about where that A is in bar 15".
3. Cracking the Whip: I've done many a 9:30 or 10 am sessions. This is a time period musicians are biologically opposed to. Take that, and add less than challenging music, and it's nap time. Keep an ear out for uninspired performances when recording fairly simple stuff. If you're working with first call players, it's not that unusual at an early hour of the day that boredom sets in. In this situation, I usually tell everyone to stop sleepwalking and give a little something to the performance.
4. Rehearsal skills: GET SOME!! I have been a spectator to a few sessions wherein just playing the whole piece over and over was considered rehearsing. If there is a specific passage that needs work, focus on that. "I'd like to hear trumpets from bar 16 to 20, the rhythm isn't tight in bar 19". I'll even repeat a single bar over and over, maybe start with a slower tempo and increase as we start to fix the errors.
5. Be clear and concise: You should have an idea of what you want from the performance before the sessions even starts. This way any questions can be dealt with quickly. Keep the answers short and to the point. Remember time is money so knowing what you want and communicating it well is important. There will always be things that may cause a session take longer than planned, you shouldn't be one of them. A Trombonist once told me "Man for your sessions, I can put the money in the meter and know I'll be out before the hour runs out".
Here's a great glimpse into a symphonic rehearsal with Leopold Stokowski, he's a pinch more serious than I would be.