Excessive String Divisi
Many composers coming from the sample world tend to use massively split up string sections. Things like triads in the violas alone, several different violin movements at the same time etc. are very common.
While this might work in the sample world, in the real world, anything orchestrated like this will suffer from massive substance problems. The rulw of thumb (of course as always with a few exceptions which would exceed the length of this tip) is to avoid to divisi strings as much as possible. Any divisi will drastically reduce the players you have per note taking away a lot of the substance of sound on each note.
It is commonly underestimated that the strings have a very rich harmonic spectrum and many of the tones you would want to split them into already ring in one of the notes you have them play already. Therefore they have a huge potential of melting together into a homogenous sound and don’t need to have every tone of the chord in every octave.
In fact, well orchestrated strings with little divisi will sound way better than even a larger string line-up with a lot of divisi when not orchestrated properly. So apart from divisi-ing the cellos (which can sustain a substance even when split into two sections) try to keep the divisis to a minimum and only when you really need it.
As a side note: one of the most unnecessary divisis in strings is to split the double basses into octaves which is coming from the piano writing where playing the left hand in octaves adds substance. With basses, that doesn’t happen. Apart from losing substance from the lower octave and moving substance into the higher octave this higher octave rings very strongly in the harmonics of the lower note anyway. So unless you have a really good reason for this particular split, try to avoid it.