Go to the library, and/or join a good book club to get set up with some decent studying materials before gettting started on your projects. After some study about maintaining proper angles when re-working triggers, sears, etc.....then you'll be ready to buy some of the needed tools and abrasive papers that can help you smooth out metal-to-metal contact.
If you don't get studied-up first you stand a good chance of causing problems.
Take care,
SS'