For sighting in your SKS / red dot:
I would suggest:
-start with a clean bore, lubed gun
-stick with one type of ammo for your sight - in
-shoot off of a bench rest (sandbags / rifle rest)
-start out at 50 yards
-use a visi-shot target (leaves a colored hole that is easy to see)
-find out the adjustment spec for your sight (example: 1 m.o.a. per click)
Remember if one click equals approx 1 inch at 100 yds, it will be only 1/2 " at 50. Also, proper marksmanship fundamentals are necessary for consistent results.
There - my 2 cents. FWIW I just bought an SKS myself and can't wait to try it out.