I'll start by giving some notes about notation. First, looking at the first page, 127 is not a real metronome marking. Metronomes are physical tools that have notches at certain points, you can't pick any number. Quarter note to 126 would be a valid metronome marking. As Luis noticed, the nat. marking has no place here. If you're preparing music, prepare one file made focusing on playback for the audio, and then another focusing on engraving for the score. If you handed that to a string quartet, they would be confused. Throughout the score, there are a lot of mezzo dynamics. Avoid using mezzo dynamics. Mezzo forte is not a "medium dynamic," it is forte but held back. It is for special cases to achieve a very particular effect. If you're using mezzo dynamics to balance, don't. Real musicians will know how to balance musically on their own. Try to have the number of measures per system be consistent and somewhat few. For an ensemble like a quartet, try something like 4 measures per system, 3 systems per page. The first page is a little too spaced vertically, and too narrow horizontally. And the final 2 measures cutting off abruptly looks quite ugly. Now to actual compositional devices. Since this seems to be written attempting to be tonal, judging by the frequent raised leading-tone, I would make sure you're more mindful to follow basic voice leading rules. For example, mm. 2-4 there are parallel octaves between the 2nd violin and cello, and this doesn't seem purposeful to me. It creates a very empty shallow harmonic quality. Throughout, the harmony is also very clunky and poorly voiced, with lots of doubled leading-tones, chordal sevenths, etc. Check what kind of harmonic function each chord is meant to have, and revoice focusing on clarity, fullness, and voice leading. The use of spiccato is odd to me. It's not wrong, but spiccato is generally paired with quicker passages, so I'm wondering if it's the effect you want, or if just a simple staccato would be sufficient. I also feel like the piece could use more direction in general. Where is it going and why? Right now, it sort of just goes back and forth harmonically between somewhere tonic adjacent and dominant adjacent. It'd be nice to hear more push and pull, and like it's going somewhere. It's sort of static as it is, give it some momentum! The piece is a good start, keep it up.