To put it simply, you can't, and you may find out later that the work is no good.
Too many trigger jobs are achieved by polishing the heck out of everything and replacing or lightening springs with little knowledge about how the gun works.
CAUTION: Gun makers add an "edge" into their guns to make for reliable functioning under adverse conditions - dirt, cold, etc. ALL trigger jobs remove or lessen some of that edge. Think very carefully before you have trigger work done on a pistol that is being carried for serious purposes. A slicked up pistol that does not work is an awkward hammer without even a claw.
I have seen a slew of trigger jobs, some done by "name" pistolsmiths that ceased working because the case hardening was ground or polished off the hammer and trigger. I have also seen ones that felt good, until some actually tried to fire the gun and found that the mainspring (hammer spring) had been made so light it wouldn't set off the primer.
Some rules: If it is too light, especially on the DA, demand that you be allowed to test fire it. On the SA, cock the gun and try to force it off cock, then try to jar it off cock. If it does either, it is dangerous.
A customer once told me that he had sent his S&W revolver off to a "supersmith" for work. The gun comes back and the cylinder won't open. Back it goes. The gun comes back again and the rear sight is missing. Back it goes. Then the gun comes again, and this time the owner takes it out and tries to click some bowling pins to death. Long irate conversation with "supersmith" finally ends with the smith yelling, "Well, gawdammit it, you didn't tell me you wanted to SHOOT the damned thing" and slamming down the phone.
I fixed the gun at a cost of a new hammer, new trigger, new strain screw, and several new springs, plus labor. Then I did a trigger job which is still fine after 20 or so years. It isn't as light as the one by the "supersmith", but then I figured he just might want to shoot the damned thing.
Jim