unfortunately, I have no idea how “experienced” you are, so maybe my experience is what you already know. However, it’s still good to know what other have experienced as well.
To be true, it’s not exactly specific for “strings”, but I will write down my general thoughts about live played stuff.
So, I remember during my studies back then, I had the pleasure to write for a small orchestra. Unfortunately, no strings were included. Piano, brass section, woods, percussion…The first thing which comes to my mind is to really know the instruments, the ranges, the playing techniques, literally everything. If you start to write, you can’t know everything from the beginning obviously, but a good starting point is to check out some great musicians online, solo interpreters, and take a good look on what is actually possible. (Here you see “how far” you can really go with your composition.)
From there, you need to remember and remind yourself, that you saw 100% of the best player, you possible can see/hear performing. What I mean is, that in most cases, especially in the beginning, low budget, whatever, you will meet people/musicians, that are not that good, not on that level. So you have two options: You either make an awesome composition, which is played mediocre or you make a “well thought out” composition (not super hard to play), and get a great recording & performance out of the quartet, in your case. Let me clarify: Even the “best” musicians are not really preparing for your recording session, as they do not have time for that. They come, play, and go. I would be surprised, if anyone would “practice” your music. Keep that in mind. They all play from the sheets and the easier it is to play from the sheet, the better the performance will be.
That said, keep in mind, that your session is not “endless”. Studio time costs money, so money is time. (You need to transform that on your scenario of course.)
What else: Know your music, and know it well. People will ask you questions, “oh, you mean it like this, or like that?”, “Could we maybe play it like this, as this is strange…”, whatever. You get the point. Just be prepared, even if this scenario won’t happen then. It will happen later on for sure.
Who will conduct this piece? You, someone else? If someone else, “the more clearer you make your music”, the better the conductor will adapt and get the right performance. As well, don’t be shy to say that you don’t like something particularly. Be kind, but as well straight forward, so people see your passion, professionalism and dedication to your music as well. That it how you gain “respect”. When people see, you know what you really want “out of them”. Not just like: “Oh yeah…that’s fine, yeah I like this…”. Remember, after the session is done, you can’t go back and fix the performance you actually don’t like. That said, recording-wise, I can only give you the most important tip: Make a short recording (pre-recording) of the theme, whatever the most important part will be in your piece. Go to the operation room, (where the console is, or the recording device, whatever the situation will be in your case), and hear this section once again and quickly decide, if you like the sound or not. This is super important, as you can’t “fix it in the mix”. You only can fix it now, not later, even not the engineer. Talk to the engineer, if you can try out some other mic positions as well. Compare that 2nd recording to the first. All in all, that will take you maybe 10 minutes, BUT, you will save your life and the life of the post-production engineer, time, money, you get this…
Maybe I forgot something, and others can add something here as well
Hope that helps