The quickest way to improve a stock trigger is to install a setscrew under the trigger in the pistol grip threads. Using the setscrew, you limit the trigger take-up by tighten the screw until the trigger is tight against the bottom of the selector when the rifle is on safe. On some rifles, this will take up at least half or more of the take-up travel before the hammer breaks. Then install shims to the sides of the trigger (at the pins) to remove the sideways movement of the trigger. This prevents the trigger from canting when pulled, and again produces a crisper trigger feel.
The hammer/trigger sear surface can be polished and the pins can be polished to take out the gritty feel of the stock trigger. To lighten up the stock trigger, the hammer spring can be tweaked.
Note: If you have a mill, then you can set the disconnector to release the hammer at the end of it's stroke, and set the hammer sear for a creep less trigger break. But this part of working a trigger over, should be left to a smith, including installing a trigger over-travel set screw.