Verify the firearm is unloaded and safe
Remove the bolt and separate the action from the stock
Clean the receiver, bolt, and lug surfaces
Check the receiver face for squareness
Check bolt lugs for even contact
Lap or true bolt lugs if needed
Square the receiver face if needed
True the barrel shoulder and threads if needed
Install the barrel with proper headspace gauges
Torque the action screws evenly
Bed the action in the stock if needed
Recheck bolt operation and headspace after assembly
Have a qualified gunsmith perform the work if you are not trained