Getting started with vintage fit
Vintage clothing online is almost always sold with the item's measurements listed. That means you have to know your measurements and know how to choose what will fit you comfortably.
Let's start with measurements. Dorothea's Closet Vintage shows most every pertinent measurement a seller might list for vintage garments. The only time you might see more measurements are in the cases of pants or swimsuits. (I'm leaving shoes and other fitted accessories for another post):
Leigh Ann of Freckled Nest posted about measuring yourself for vintage. I strongly urge you to follow her suggestions, including wearing your bra. I also would add that getting a friend to measure helps with accuracy, and is imperative for getting accurate length measurements, and your shoulder width. Leigh Ann doesn't stress lengths, but your waist length (base of neck or shoulder to waist, measured in back) will eventually be very important in choosing vintage.
Allow me to digress a moment here. You can be any size and look great, you just have to be honest about the size you really are. As Leigh Ann wrote about measuring your waist: Don't suck in or you'll have to live that way and you'll turn into a fish. Be honest because the result will be you looking good. If you lose that weight you've been meaning to lose or whittle your waist with exercise you can find a new vintage item. Now is now. There are vintage foundation garments that can change your size somewhat, but that is more advanced material. We are starting out slowly.
Of course, if you are lucky enough to have a vintage clothing store in your town, you can try things on for size. Still, it helps greatly to know your measurements to begin with.
Now, what vintage garment are you going to look for first, remembering we are taking this in stages?
My suggestion is a sweater, because 1. a sweater's fit is flexible and 2. vintage sweaters are the best!
Next: Choosing a vintage sweater