As with others I do a bit of trial and error. I am lucky to have a gold standard with the bike I have been riding for years. Anyway I will take the new saddle (adjust the height and for/aft position first) and then take a long straight edge (like a board) which extends from the saddle over the bars. I set the tilt such that the height of the bar is the same as my gold standard bike - if all other adjustments are the same that sets the saddle angle the same within my ability to measure it. Then I get on it, if there is any pressure from the nose of the saddle I tilt that down until it is gone, if there is any tendency to slide forward when my hands are on the hoods or in the drops I tilt the nose up. I can usually feel just where my sit bones need to be. Then I ride about 40 miles with my wrenches in the back pocket. Fine adjustments are made along the way based on my feel. I will also make any up/down adjustments based on what my knees are telling me and if I tend to rock in the saddle at high cadence. At the end I will recheck the fore/aft position by using a plum-bob on the knee at mid-pedal, if it's OK I'm done, if not I will iterate again. I usually have it dialed in after the first ride.

For me - the fit one gets in the shop is just a starting point, the real fit occurs on the road after many miles.