If you want to wear vintage, look in shops that have vintage in the name or description. You might find vintage pieces in second-hand shops, but what you will mainly find is just old clothing. In vintage shops, you will find a curated collection of pieces and a knowledgeable owner to help you.
If you like pieces from several eras, go for it. But focus on accessories that you can pair with your contemporary clothes for a touch of vintage rather than mixing up several bygone styles.
A word about size: Women’s dress sizes have changed significantly over time. A rule of thumb is that a piece of clothing from the 1950s or ’60s is marked 4 to 6 sizes larger than modern sizing. So for example, a dress from that era that is a size 12 would be approximately a size 6 today. So don’t freak out about the size on the label. As you get closer to the current time, for instance, a piece of clothing made in the late ’80s or ’90s, you can expect that sizes will be more in line with what you wear now.
Always try a piece on to be sure it fits before you buy.