The key is to maintain a balance of frequencies while keeping at least some to a traditional orchestra layout.
Traditional orchestra is Violins 1 & 2 on the left, Violas more in the middle, and then Cellos right and Basses to the right. But when mixing, it's also common to keep the basses closer to the center. Making frequency space while somewhat keeping to this layout is most common. For a light string section sound, it's common to omit the Bass section and just use the Cellos or Violas on the bottom. Otherwise, Cellos and Basses most often double the same bass line an octave apart with a traditional orchestra.
https://soundcloud.com/peter-cavallo/within
In the above recording, Peter has his piano mixed fairly wide. The high piano notes are clearly heard right of center, so it's the player audio position. Note the amount of reverb on the strings so they sit more in the back behind the piano. The only improvement I can think of is during the more full string parts the dynamics with the piano could have been a bit more, but notice how you can still hear the piano during the heavier string parts. It's about frequency positioning during the mix.
https://soundcloud.com/peter-cavallo/the-morning-after
With the above example, you can clearly hear Peter's piano mixed more to the right, allowing the Cello to fill the rest of the space. Sounds like Violas come in later in the center very dry (I would have preferred a bit more reverb to move them back a bit, but it still works). He went more for a chamber sound with this one.
So indeed, it depends on the sound you're going for on how you arrange and mix it.