I always inlet the trigger and plate before shaping. Find your centerline on the bottom of the stock, look at where the sear arm is, fore to aft and vertically, and sort out where you want the trigger pinned (on your blueprint or plans, ideally). The pin is going inside the lock mortise and will be covered by the sideplate, when I do it. I like to have the trigger pivot pin positioned at the same level or above the sear arm, and not too far forward. Not more than 5/8", not less than 1/4" forward of the sear arm. A lot depends on the height from the pin to the "shoe" of the trigger. If too far forward, a heavy pull results. Too close, and the trigger must be pulled some distance to let off the sear, causing "creep".
Now figure out where the trigger plate will go (if you have one) and how the tang bolt will join the tang to the trigger plate. Obviously the trigger "blade" must pass through the slot in the trigger plate.
Once you have layout planned, scribe on the belly of the stock where you need to inlet the trigger itself. Drill 2 holes, one at each end of your scribed mark with a narrow drill about the thickness of the trigger "blade" and remember you don't want to go deeper than necessary. I then use a wide thin chisel to stab straight down in the rectangle of wood to be removed, then take out the wood with a curved, very narrow chisel to depth. Keep the inlet tight and smooth and the trigger will be well supported and not rub. Generally it is necessary to adapt the trigger blade (file it down) to just engage the sear. Once the trigger is where it needs to be, inlet the plate. Then I drill for the pivot.
