when you clean your bolt make sure you take the firing pin retainer pin out, remove the firing pin, and clean the firing pin channel.
when you reassemble, make sure firing pin channel is dry so that debris cannot accumulate to sieze the firing pin, which may potentially cause a slam fire. In all other cases, the sks will not slam fire because the force of the floating firing pin moving that tiny distance int he channel does not have anywhere close to the amount of momentum required to deform the primer, even "soft" primers
Everyone hears about these supposed occurances of sks slamfires, especially in the states where they're less common, but no one every saw it in person...