Guide to Tailoring

What you have to keep in mind are the characteristics of a tailored garment, what a jacket always has: a rolled collar, lining, a straight-cuffed sleeve, and a lapel (which is the front of a coat; a continuation of the collar). After understanding what a tailored garment always includes, being familiar with the quality of standards always helps. First off, it should be fashionable and have an attractive fit on you. Having the proper waistline, length, sleeve fullness, and sleeve length appropriate for you and your style.
The jacket should fit smoothly over your undergarments but have an appropriate amount of ease for the body movement; making sure that the neckline and the armholes fit your body without gapping or straining. Dart and design details should be properly placed as well as the shoulder length, unless your pattern calls for a dropped shoulder. Besides the fabric, choosing a pattern may be one of the trickiest parts because of the many styles and trends out there.
Avoid styles that you have never worn before, choosing one that suits you in a flattering style, length, and fit and select a pattern designed for tailoring, Make sure to buy the same size your normally would because companies already add in the ease for people sewing with heavy or thick fabrics. If you want to be extra cautious you can add “in-case” seams on the existing pattern. There are other fitting techniques and alterations you can do if your jacket doesn’t fit right.

If it is too big, you can include or increase the size of the darts, fold out excess fullness/fabric to make an area smaller, redraw darts and/or seam lines, or slash and overlap the fabric to decrease dimensions. If your jacket is too small, you can slash and spread the fabric to increase dimensions, decrease the size of the darts or take them out altogether, or just add fabric. Although if your jacket is too small, it may not have the desired look that you want after the alterations, so be careful.
Lastly is the fabric, another hard part. The very first thing that you want to do is choose a fabric that is appropriate for the style you have chosen. You want a fabric that is heavy enough to give your garment body and shape but one that can also be molded (can be tailored easy). Be aware of fabric nap (so stripes/prints/patterns). You can use these fabrics but make sure you buy enough so that everything matches. Keep in mind that when all the fabrics are put together, you want your garment to look natural and not to stiff.