What is the one thing you would do to a new rifle to make it more accurate?

Well the first thing I would do is take it out of the box. All that cardboard makes it hard to shoot. Seriously though most brand new rifles could stand a trigger job. The problem is most come from the factory with stiff triggers to make the lawyers happy. The other thing you can do to make a brand new rifle more accurate is shoot it. Some rifles shoot better after a few boxes have been run through them. It smoothes out some of the tool marks in the rifling.

Shoot it, clean it, polish it, look at it, carry it around the house like a new baby.....shoot it some more and put it away clean.
Then....trigger job (will help), try upward barrel pressure near the end of the stock
(might help, or make it worse, worth a try), try several different style and types of factory ammo or handloads and keep records of the targets. Other than dual pillar bedding and/or glass bedding it and/or floating the barrel there' s not much else to consider.

Have my smithy build it from scratch.

Factory rifles, I' d have to agree, NEED trigger work, at least adjusted (in new savages and Win 70' s). It' s rather ridiculous when you think about it, but a heavy/uncomfortable trigger pull can hurt your ' shooting accuracy' a great deal (I say ' shooting accuracy' since the rifle hits where you aim it, you just can' t aim it where you want, so it' s not that the rifle is ' inaccurate' ).

glass bed the action and free float the barrel.....If it don' t shoot I won' t waste my money on the trigger work.

Glass bedding and free floating won' t do you a bit of good if the trigger is too heavy. Besides some rifles don' t like to be floated and some are already pillar bedded.

Not all guns need to be worked on so first I determine if it does before I fix it

friz, you shoot your guns, and I' ll shoot mine!!!