My previous comment aside...
The big wins for squeezing a bit tighter group out of the SKS are:
a) shimming/bedding the action. I took an inch off my group size by doing this - I used waxed paper folded and ironed out and then worked in while it was still warm and pliable.
b) trigger job : Haven't done this myself, yet, but the trigger on the SKS is... Russian. There are a few different methods of taking out the creep and lightening it a bit. This won't change the inherent accuracy of the rifle, but it will improve the practical accuracy. Fighting against a heavy/creepy trigger is not conducive to good groups. I learned the hard way that if I'm going through a few different rifles in a day at the range, not to do things like go from a K31 to an SKS... After shooting a K31, you really notice how bad the trigger is on an SKS, and your groups will open up a lot. At least that's true for me.
But, if you're already getting 2-3" groups with an SKS, that's actually quite good. If you start messing around with shimming and bedding the action, you might end up actually making things worse.