In my mind this starts happening as soon as you take the pieces off your cutting table.
From that point on I try to keep my construction vertical (as I am most of the time) and in a training situation to be a round shape.
This means that between pressing and sewing sessions I either hang up pieces or, better still, pin them to my dress form. I had an idea a while ago to experiment with draping but that stopped when I realized I am not particularly interested in draping, so I use my dress form as a place where my pieces can practice being a garment.
I feel that you can't take flat fabric, press it flat on an ironing board, and then expect it to be successfully round the rest of its life. Your fabric has to learn those days are over and there is no time like the present.
Of course this brings us back to pressing and another essential pressing tool, the tailor's ham.
Here is mine:
Now this one, as old as my serious sewing, has a couple of curve variations, but really I use the end and the concave side the most. It has a wool side (napped) and a cotton side. I suppose you could make your own if you had a source for hardwood sawdust and could pack it tight enough into a shape but that would be about as easy as putting on support knee socks IMO.
The point is whenever you have sewn a seam that is not perfectly straight - princess seams, some waistbands, darts - so many things - you will get a better press if you position your fabric over a matching curve.
Oh and because I haven't mentioned it before and should have, once you have that heat and steam in your fabric don't move it until it is cooled. That will give your fabric a chance to set the press.
Tailor's hams are also enormously useful when making collars, particularly those with wool or fabric with some memory to them.
You can set your ham up vertical in a ham holder (you can use cans or, like one woman I know take it to the garage and put it in a vice on the workbench) and treat it like a fake neck.
Wrap your collar around the ham like it would be when you are wearing it.
Note that this will probably shoot the under collar out a bit when you roll the long collar seam under so it won't show - just cut the extra off, this means when you sew the collar to the neck edge the seam will stay hidden - never be a slave to matching the cut edges when you are in the make flat round process.
Back to the ham/neck.
Once you have this set up take your iron and shoot that little unit full of heat and steam and leave it to dry.
This will give you a beautifully shaped, already pressed collar to insert into your garment - with a nice professional press you absolutely cannot get when you are ramming it into an ironing board and hoping for the best.
This is what steaming it on a ham looks like: