These, like nearly everything I write, are primarily the result of my own observations after decades or working with sewing students and in sewing for myself and my family.
Here we go:
There is a lot made of the big three- bust, waist and hip - but IMO some of the most potent body parts, when you are working towards fit, are lesser known measurements, or shapes.
1. Shoulder slope. I talked before about the importance of getting a good upper body fit by working with the chest/high bust measurement rather than a bustling but as important as fitting the hanger is knowing what the shape of the hanger looks like.
Some women have your so-called average shoulder shape for which average patterns presumably fit, most of us have shoulders that are either square (like mine, boney and they just go straight across like a ruler, detected by collars that seem to ride up) or sloped (if you have always thought you have had "small shoulders" in fact your shoulders might just be sloped, think duck, not trying to be rude here but need to give you a clear image) meaning your tops seems to just hang too loose on the shoulders or even feel like they are sliding down.
Look for where the extra fabric is on your shoulders.
If it seems to be bunching up at your neckline, particularly at the back and your collars seems to stand away from your neck you might have square shoulders - basically the pattern is providing fabric where there is no you.
If you feel you have extra fabric deposited below your shoulder line and just too much hanging off your shoulder you probably have sloping shoulders (a good look in the mirror at your bare shoulders will actually tell you everything you need to know here).
My good friend Debbie Cook at Stitches and Seams does a nice easy description here of how to do a fast easy pattern adjustment for either of this issues.
2. Arm length. Actually no human measurement IMO can vary as much as arm length which seems to have nothing to do with your height. It's easy to measure on a set-in sleeve pattern, straight down from the shoulder notch to the wrist. Many folks need sleeves shortened.
3. How high and low your fullest part. These would be the three Bs - bust, belly and butt. Bellies are often higher than patterns think and busts and butts lower. This matters because your darts- bust, front and rear- need to end about 1/2" or more bit before the fullest part and aimed right at it.
It's pretty simple really- the darts pick up fabric where you don't need it and release it where you do.
If that extra fabric is released too high, too low or too early or late you are going to get an unattractive bubble sitting in the middle of nowhere. Shortening and lengthening darts is easy, just move the last dart marking in or out, in a skirt or pant waist dart this just makes a shorter or longer dart (I personally lengthen all my back waist darts about 1 1/2" which is all you need to know about gravity and me).
In the case of a bust dart you can both move the dart end in or out so it is about 1/2-3/4" from your nipple (the more fitted the garment the closer the dart end to the bust point) but you might also have to raise it, or more commonly for larger busts lower it, so it is aiming at your nipple and not some random spot on your chest. If you do this of course you will have to redraw the dart legs so the lines from the side seam are properly aimed at this new end point.
I apologize here for not offering tons of great and useful pictures for all you visual learnings out there, but that would require far more time than I have right now, hopefully my words are clear enough, and if not let me know and I will try again.
Of course too you don't need to put a dart where you don't need them. For instance if you have a full tummy and basically your waist goes straight down and right into it, you don't need a front dart at all in fitted skirts (not sewing your darts will also add greatly to the fabric available for your front waistline too) or even only a small one.
Remember darts are for shaping and not necessary in cases like this where there is no smaller part to be released to a larger one.
All of this brings me now to the really, really important facts of pattern choices.
Because you have shape and it is an individual shape, you are going to have to add (see previous post about making larger not making smaller for the pattern size chosen). The basic rule of thumb is to compare your pattern's ideal measurements and your own and add the difference to the seams.
Classic example would be you have a 34 inch waist and your pattern bought for your smaller 40 inch hips says the waist in that size should be 30 inches. This means of course that you have 4" to add and with two side seams this would be 1" added to each (2 X 1" for the front and 2 X 1" for the back), tapering in the top of say your skirt with this addition to the pattern's hip.
The principle applies for additions everywhere in your pattern but the big trick is that the more seams you have to divide these additions among the more subtle and successful your pattern alterations will be and the more able you will be to target them.
Listen to this, it's important, the more seams you have to play with letting out here and there taking in where you might need to in areas where you have hollows like the front of your chest or at the back or your neck where it slopes forward, the easier it is to fine-tune fit.
By contrast a seemingly "easy" few pattern pieces pattern can be a fitting nightmare because there are no shaping features for you to work with - and instituting those, adding seams or introducing darts, are fairly sophisticated and very easy to mess up.
On this basis princess seams (all those places to adjust along their length, so easy to make room for a large bust exactly where the bust is larger and return to a smaller upper chest) are terrific for fitting (enlarging darts is so much harder), as are two piece sleeves (smaller armhole and bigger biceps, smaller wrists) or panel seams in skirts and pants.
Sometimes nothing is harder to fit than a "simple" to sew pattern.
Does this make sense?
The pattern below is hard to fit, only places to add anything is at the side seams and that might not be where you want it. What about a full bust or hollow chest?
In an exaggerated contrast look at all the pre-set places you have in this pattern to adjust, you could make this one fit anybody:
|See the fitting difference between view B and the others?|
|Far easier to get a smooth fit here than with darts|
Folks with sloped shoulder for example do well with raglan sleeves, and folks with square shoulders with set-in sleeves:
Enough to think about now.
To be continued.