sounds like you have an inconsistant cheeck weld...which varies the sight picture.
i do the same thing with my ak-74...put my nose on the receiver/action cover button.
depending on the position you are in (prone, sitting/kneeling, offhand), cant, or tilt, of the rifle will also play havoc with your point of impact.
i suggest you get a turner or les tam sling and learn to use it for prone and sitting/kneeling.
for devoloping consistancy of sight picture and a calm shot release, nothing beats dry firirg and lots of range time.
you do not mention which rifle configuration you are using, but the basics are the same. getting a few good books a learning the classic shooting positions is a great place to start. while everyones' hold is slightly different, the fundamentals are universal.
try this: get into your position and relax as much as possible. pull the rifle into your face...try not to tilt your head into the rifle. the more vertical your head, the better. pull the buttstock into your shoulder firmly, but trying to keep muscle tension as low as possible. keep the buttplate as high on your shoulder as need be.
grasp the handguard loosely...exerting no tension on it...it should just lay in there.
trigger finger should not "drag the wood"...only the pad of the finger should touch the trigger. the pistol grip should be gripped firmly...but again, not too tightly.
muscle tension causes decreased accuracy.
concentrate on finding your natural aim point. DO NOT TRY TO STEER THE RIFLE! there are various excercises to improve your natural aim point.
getting a sight picture varies widely among shooters. with my old eyes, i don't have all day to dress a bull...i have to take the shot faster than a young man.
run your focus from target to front sight to rear sight to target to fron sight. focus on the placement of the front sight as you approach shot release. your "computer" (brain) will automatically center the rear apeture.
these are just a few basics. hell, entire books are devoted to each attribute of accurate shooting.
see the fellas in the competition forum...there are some very helpful shooters in there.
good luck.