Many are the tomb paintings you will find reproduced. Quite a few are the scholarly discussions of how styles changed down the centuries, both in hairdress and garments. Not at all will you find anyone going out on a limb, trying to figure out how the garments were cut or held on, in any detailed or practical manner -- until you stopped here.
Most ancient Egyptian clothing is of the draped and tied variety. A few items require sewing beyond hemming, while two or three are very sophisticated indeed. Notable among the last are the gloves found in tombs. These apparently served to protect the sacred-royal wearer from profanation by the mundane world, and reduce tanning, so as to preserve the youthful beauty of the skin. So if the Egyptians stuck to one-size-fits-all draped clothing, it was by aesthetic choice, not because they were unable to manage complex shaping. Much the same can be said of the Indian woman of today, who largely eschews European complex fashion for the ever-beautiful sari.
First, you must remember that to the people of the Nile, nakedness is the natural state of mankind, and is viewed with no horror or revulsion. Neither is it viewed with particular sexual interest. A famous line of a tale has a man suggest that the object of his desire put ON her wig, jewelry, and makeup, so that they can go have sex. Children ran around naked until they were thoroughly housebroken (it's easier to let them go in a corner of the yard, or clean up a puddle on the dirt floor, than to do diapers). Girls of about seven or eight seem to have graduated to the basic gown, while their brothers would probably wear a loincloth only on dress-up occasions. Workers of both sexes shed their clothes for hot, sweaty, or dirty work, and no-one thought anything of it. Admittedly, one sees women less in the nude in art, but as any woman over puberty was potentially pregnant, they were generally spared heavy labour. They are also portrayed as fairer-skinned, indicating far less outdoor work than their brethren.
Female dancers often perform wearing only a bikini bottom with an embroidered hipband, jewelry, and garlands, but this seems less to be sexually exciting than, like modern performance dancers in leotards, to enable the lines of the body to be seen. Not but that the gentleman didn't enjoy the sight, I'm sure.
One garment seen everywhere is often called a loincloth, but it does not wrap close around the lower body. Instead, men wear it as a simple skirt, which word of course would never be applied by the original (predominantly Victorian male) Egyptologists to a male garment. But that's what it is.
The version worn by upper-class men has often baffled archeologists, due to a fancy triangular section in the front. Unable to shake the idea that ancient people lived in animal skins, some have suggested this was a leather attachment or apron, ignoring the fact that animal products were often ritually unclean, and that people in hot climates do not develop leather clothing: it's too uncomfortable.
By serendipity, I happened to see a neighbor going out to get his mail in what is locally called a "lava-lava," and realised that if it were in plain white linen rather than bright orange with purple hibiscus blossoms, it would be the long-baffling upper-class skirt, complete to the triangular section hanging in front. This is merely a length of cloth, not too wide, enough to cover from upper hips to knee, and long enough to go around the wearer about one and a half times. Like any tied-on garment, on a man it is best fastened around the upper pelvis, tightly, so that it can't come loose. Think of how the belly-button usually shows in Egyptian art. One upper corner is knotted with a handful of upper edge, wherever will make it tight, producing the ear of knot seen sticking out in many a painting. A further hand's length or so of the upper edge is tucked into the waist, providing overlap. The remainder of the upper edge, hanging down, is the front edge of the triangle. That loose upper corner is the lower angle of the triangular area. If you heavily embroider, applique and/or bead this triangle of cloth, it will hang exactly as the tomb paintings show.
The actual loincloth is the usual strip of linen, put around the back of the waist, knotted in front, the ends brought between the legs to cover the lower body, and tucked through the band in the back. You will see workers wearing this, sometimes with a very skimpy lava-lava that doesn't meet in the front, but is more a scarf tucked into the loincloth waist.
The other garment you will associate with men is the headcloth, sometimes called by the Arabic term kefiyeh, though it is shaped, worn, and fashioned nothing like a kefiyeh, other than that it is on the head! The crudest form is a rectangular scarf, one side held against the forehead, the two adjacent corners tied at the nape under the other edges, which float free. I have seen the same thing done with bandannas by carpenters or housepainters in hot weather.
On a slightly more advanced level, the headcloth is a semi-circle of cloth, tied on the same way, the fullness draping in attractive flutes. At the extreme, this becomes the King Tut striped headdress. Here, I believe, a long band was attached to part of the straight edge, and its loose ends used to tie on the headcloth. The free part of the straight edge is brought forward to hang down onto the chest. The semi-circle is then cut and hemmed in a complex curve so that it will just touch the top of the shoulders, but hang much longer fore and aft (alternately, the excess may just have been tucked inward on top of the shoulders). The change of the stripes, from horizontal in the front to vertical in the back, is one of the clues to its structure, resulting from laying the straight edge perpendicular to the woven stripes. In many representations, the headcloth appears to be held up by something more vertical than the skull, at least around the front. This is the stiffened attached band, or perhaps a gummed linen insert. Anything like a uraeus was then fastened over the cloth.
See the pictures.
When it comes to women's clothes, one must remember that the stylizations of Egyptian painting is often misleading. One must rely on sculpture. For example, thanks to painting the Egyptians were described as using a vertical frame loom, until an ushabti group of a weaving shop showed that the frame was mounted horizontally. Thus, while painting will show a woman's breast bared by the straps of her gown, you must also note that her eyes point out of her head at right angles to her nose: this is not realistic. In no sculpture does a woman's gown ever bare her breasts. Those wide straps serve the support function of a bra. So forget any "artistic reconstructions" you may have seen that put the straps between the breasts. They are misled, and under-researched.
This narrow sheath gown does present one problem: how it fastened. It is always shown clinging like a spandex tube, two sizes too small. However, Egyptian sculpture also had its stylization: clothing is shown unrealistically second-skin. For example, a king will be shown in a lava-lava sprayed on, though by other lines indicating pleats it must have been linen.
Just as making a house or bridge stay up has certain requirements of support versus load, so all clothing has its engineering limitations. For a woman to walk normally, as she would without constrictive clothing or long training, any skirt must be six feet around the ankles. I made a long dirndl-cut skirt once out of a five-foot remnant of gorgeous fabric, and nearly hurt myself at least twice every evening I wore it, from being pulled up short.
So the average Egyptian woman is going to require a similar hem-to-height ratio in her sheath gown. I am here suggesting a cut for minimum waste in square-cut narrow-loom cloth that will reduce gathers at the top. Nonetheless, there must be some, in order to get it on over either the head or the hips. I suggest that this peasant-commoner woman probably pulled up the excess with a drawstring in the top hem, just where the straps attach, tying it between her breasts and tucking in the ends.
Back to the pictures.
Upper-class clothing frequently proclaims itself by its impracticality. Noblewomen may have tottered along with an artificial, tripsy gait, brought on by a four-foot hem. They may have been sewn into their gowns by their servants. They may also have been indistinguishable in cut from a peasant's gown, relying on the fragile finess of the linen to make the difference. This we cannot tell, as I have never found a representation of a woman getting dressed.
The last garment you will see with any frequency is a transparent overgown worn by men and women of the best society, often called "the royal haik" after the haik of North Africa. In fact, it drapes and fastens nothing like a haik, which is held on the shoulders by a pair of penanular brooches linked by a chain, and belts itself. The Egyptian overgown is tied in the center of the chest, and forms pseudo-sleeves over the upper arms. It is always shown pleated in those fine knife pleats so beloved of the New Kingdom upper classes.
It has often been suggested -- or stated -- that this was done by broomstick pleating, but bouncy, mushrooming broomstick pleats do not give the right look. The proponents of broomsticking point out as obvious the "fact" that no-one before pleating machines could possibly have devoted the necessary days to making individual pleats, even with pressurized steam irons. Such persons ignore the fact that a noble of the court could have a dozen slaves with nothing better (and quite a few things worse) to do than to spend all day "ironing" pleats into linen with a smooth marble or glass "linen pleater" in the manner of European peasant women who went in for fancy pleated linen headdresses or skirts, and assuredly did not broomstick them. In some parts of Slavic Europe, they literally chewed the pleats into an ankle-length skirt (I have spoken with "old grannies" from Croatia who have done this; it is not rumor or anecdote).
So all the pleated clothing will have been just as evenly, flatly, and regularly pleated as the art shows. If a peasant woman can take the time out to knife-pleat her festive dress, a crew of clothing care workers can do it for the every-day garments of the nobility they serve.
When the lava-lava or overskirt is shown in the transparent knife-pleated fabric, note that the lines of pleating go across the buttocks, rather than hanging down like a kilt's pleats. This allows the stable edge to be tied around the body, without the stretchiness of the pleats to interfere, or else be stretched out of existence, or require stay-stitching. It also clings to the derriere, showing off a lean, muscular rump.
With this much information, and a study of Egyptian fashions OF YOUR PERIOD (they do change), you should be able to get your characters dressed and undressed authentically.