Need help with trimming fenders, beating pinch welds

I know there are many threads on trimming liners and fenders, however I am curious as to what techniques and tooling will provide the best results. Other members who have trimmed their fender lines (specifically the plastic right in front of the fire wall) what tools and techniques did you use.

Also for those who have hammered their pinch wields, what did you do afterwards to prevent rusting.

Once again I apologize for bringing up an entirely new thread on this subject, however I want the job I do to look professional and not just wing it.