On a regular semi-auto trigger job, you reduce the sear engagement, and then retime the disconnector. When it's done, those parts are unique. I had a trigger job done on my Mini 14 by Gun Doc. He's a great smith, and has a reputation as the best Mini 14 trigger guy on the planet. When I got it back, it had a light, crisp single stage feel. I was thrilled until I took it to the range, and found that it was doubling. Had to return it, and it came back as a dramatically improved 2 stage, and the doubling is gone. All of the adjustments were done by filing/stoning parts in the trigger group.
You pretty much HAVE to do it that way in a Mini because of Ruger's paranoid policy on FCG parts. On an AR, you can get one with screws. I have a cheesey (Jard) in my varmint AR that has a creepy 1 lb pull. It is barely OK, and WILL get replaced with better parts some day. No way I would have that thing in one of my 16" guns.
You can also reduce hammer spring tension, which relieves tension on the sear as well. I makes for a lighter pull, but also reduces the force on the firing pin and increases lock time. There is a safety margin built into hammer spring tension, so you can get away with some reduction.
Stock AR triggers suck, but they always work within the manufacturing tolerances used. An experienced guy can work within those sloppy tolerances and make major improvements. The other option is to replace the floppy parts with precision ones. Replacing the parts almost always costs more. It's also probably a little safer and reliable.