The following article comes from an amazing website, La Couturière Parisienne. It is well illustrated and better than anything I could do (since I cheat in my 18th century design by using hook & eye tape for the front closure). I did re-word some of the passages to make them clearer, in my perception, but it is very close to the original, to which I give all the credit.
How to Dress in 18th century style
For decency reasons, we start with a lady who already wears her shift, cap and stockings. Can't be having pictures of women without a cap on, now, can we!
The over-knee stockings are fastened with garters just below the knee. (To learn why it is tied below the knee and not above it, see The Stocking Page at La Couturière Parisienne.)
If she hasn't done so yet, the lady now has to put on her shoes, unless she intends to wear mules (as she does here) or has a maid who will fasten the shoe buckles. As soon as she has the stays on, she will hardly be able to bend down to fasten them herself.
Now would be the time to tie on the decency skirt or under-petticoat. (In the pictures, it was left out for simplicity reasons.)
Then, the stays come on. Remember to use spiral lacing! Before tightening the lace, pull the shift straight so that its neckline sits just right. See to it that the shift fabric is distributed evenly all around. (Find more information about putting on stays here.)
To make sure that the hoops do not show through the skirt, one or more petticoats should be put on top. They don't have to be very thick, quite the contrary: they should be light, except perhaps in winter. A large number of folds and the stiffness of the fabric hides the hoops best. Therefore, the under-petticoats should have as much fabric as the visible petticoat. Two petticoats of light fabric work better than one petticoat of heavy fabric.
Now the visible petticoat, the skirt, is put on. The waistband is in two parts (same as for the under-petticoats, by the way) and long enough that each half goes all around the waist to be tied in a bow. The back half is tied on first...
... and then the front half. This allows the back and front half of the skirt to overlap each other, allowing for changes in a person's girth or for use by more than one person. Since the front half lies on top of the back, the pocket slits are easily accessible from behind even if there is a considerable overlap.
Next, the stomacher is fastened to the front of the stays: it is pinned on using the flaps on the side of the stomacher.
One question I am often asked is "Was this not dangerous?". Well, when putting the needles in you do have to be careful not to go to deep, lest you either hit the boning and break the pin off, or worse, miss the boning and hit the flesh! The pins should be put in vertically, shallowly, and the tip should come back out the fabric flap. If the stays are stiff enough, this will happen almost automatically. As the robe will be on top, the pins will be well hidden both from sight and from skin.
Now the robe comes on; it is put on like a coat. The front edges are placed onto the stomacher and pinned to it. The best way to do that is to fold away the dress, place the pins underneath – as close to the front edge as possible – and then fold the dress back to hide them.
These needles, too, aren't dangerous if they are put in shallowly from the top down and hidden under the gown. Just to be sure to have the tip go very shallowly back out through the fabric. It is a higher probability that you will scratch yourself or ruin your engageantes by brushing them against a pin tip lying outside the fabric than there is of driving a pin into the skin of your torso. The stays will protect you from the pins.
A woman of simple means would wear a jacket rather than a gown in everyday life. The jacket is often a shorter version of the dress and is put on in the same way.
When wearing a robe à la française, a close fit must be provided by tightly pulling the strings hidden under the back pleats of the dress. Pinning the front edges is easier if these strings are loose. Now is the time to have them re-fastened by a maid. This is another feature that makes the française so well suited for more than one dress size. My model here is at least two sizes away from the person the dress was originally made for.
But what if it is really cold? I have not found much in the way of winter clothing yet, but I suspect that both mantelets and pelisses were not just made of taffeta, but also of wool and possibly, lined with fur. Commoners may have worn knitted triangular wraps as well.
For Society occasions, the fichu was left off, an elegant hairdo replaced the cap, and of course, the lady would put on a silk robe rather than this relatively simple cotton one.