There are 3 kinds of main sleeping positions: sleeping on the back, sleeping on the side and sleeping on the stomach. Each of these has further sub-variations but when we discuss snoring it is sufficient already just to stay on this higher level.
Understanding the sleeping positions and their impact on snoring
So keeping in mind that snoring is what we call the vibrations which occur when our breathing channel is blocked or inhibited one way or another, we look at the sleeping positions from that perspective:
Snoring on the stomach
Sleeping on the stomach is probably the least favourable option if you are aiming to prevent snoring. Just by the definition of the position your face is in the pillow or the neck is twisted to the side. Either way, it is clear that this is the position where it is the hardest to breathe as the stomach can not easily go up and down and as it is hard to intake air if the face is in the pillow. And as far as preventing snoring this position is the worst.
Snoring on the back
Sleeping on the back is the 2nd worst position for a completely different reason. People tend to snore on their backs because the gravity is pulling down the tissues above the windpipe and pressuring it thereby reducing its size and making it difficult to intake air. So this position, even though more favourable than the stomach sleepers, is still very bad choice when it comes to snoring.
Prevent snoring by sleeping on the side
The final position, sleeping on the side, is by far the easiest of the snoring solutions and the reason that it works is because when you sleep on your side and especially if you have a good pillow then your spine is aligned with your neck and your head in a straight line and this allows the air passage to stay open even if your muscles are relaxed at night and just by sleeping on your side you could prevent snoring from happening or, at the least, reduce its loudness and frequency.