One of the best things you can do to a trigger is polish contact points. There is a lot of talk about not polishing the sear engagement areas due to changing the angle of contact. If you set it up in a jig that holds the angles and go real slow, you can make the area shine without disrupting the angles at all. I have often used different grades of wet and dry sand paper glued to a flat metal piece.
After the sear, the other points are important also. It is a great rainy day job.
By a spring kit with as many assorted springs as possible and do some experimenting there also.
When you are done, be sure to load the gun and give it a few sharp raps in a safe direction of course to see if the sear holds. If not, readjust any screws or go back in as make necessary changes to finally end up with a safe gun.