Here is my garment fitting process with a fit model (pre production). I have been working as a fit model for 8+ years and also as a fashion designer. I have been to countless fitting rooms and factories in NYC all along 7th avenue. Here is the method to create great fitting pieces that your customers will love.
After you drape, pattern, and sew your first sample, you are not done! The KEY to selling anything is the fit. Clothes rarely fit off the dress form and pattern table. You need to fit it on a human fit model that is similar to your target customer.
Once you have your first samples, measure all the key points (like bust or waist circumference, shoulder length, sleeve length, sweep) to have a record of what you received from the factory.
Why spend time doing this boring task? Sometimes the factory makes mistakes or it shrinks during a steam. You don't want to give them feedback on the pattern if the pattern does not match the sample.
Take those discrepancies into consideration in a fit. If the sleeve length came out too short in the measure, don't tell them to lengthen the sleeve based on the fitting. Tell them to go back to spec, your original intention.
Have your fit model try it on and take front, side, and back pics.
Have your fit model walk, sit, and generally move.
Ask your fit model, how do they feel? You are looking to gauge if the garment is comfortable. No one wants to change the fabric or stitching at this point, BUT you need to know NOW rather than sew thousands that the customer will not buy.
Have the model stand straight, with her body weight evenly dispersed on both feet.
Check if there are draglines or if anything is out of balance.
If there are tension points, cut at the seam line let it fall open. Measure how much fabric is needed at that point (end-to-end).
If there are bunches or baggy areas, pin or cut away the fabric at the seam lines
If there is twisting, check if the fabric naturally torques when the model is no longer wearing it. If not, the pattern is out of balance. Cut the pattern horizontally, shift it based on the depth of the fold.
Check the closers like zippers and buttons to see if they work.
Check the pockets to see if they are placed in a natural place and if the pocket bag is the shape of the hand.
Let your fit model verbalize any concerns or provide feedback to improve the garment. They likely feel something you don't notice!
Check the design. Does it look like the sketch?
Repeat this fitting about 3 more times until the fit is good. The last fitting is your pre-production fitting and should just be a check that the pattern is correct. There should be no modifications at the last fitting!
Now you are ready to mass-produce knowing you have what the customer wants!