There are no easy pointers one can impart in a few lines. If there were, there would not be so many repro pieces made and sold daily.
It takes a discerning eye (and sadly some of us perhaps even with trying may not ever master the ability) + decades of experience to begin to acquire some confidence in the business of authenticating true antique jewelry.
If it’s true antique pieces you are after, unless you are a seasoned antiques dealer/expert yourself, stick to true and true shops that only sell antiques or are reputable in disclosing antique-style reproductions (ie Lang’s), and pay the premium to get that piece of mind. There’s a reason why you pay more at shops like Lang’s: you are paying for their experience aka the experience most of us don’t have.
Otherwise, it’s always just a gamble and only you can decide how much you are willing to gamble.
I’ve only dabbled in antique jewelry for the last few years and I can humbly tell you I’m not much wiser than where I began.
I’ve been duped (have bought glass coated beads sold to me as pearls, dyed quartz sold to me as emerald, so on) and paid the price of my tuition (but nowhere done paying tuition I’m sure!), and me thinks that I can spot some reproductions at this point, but I’m not willing to gamble $$$ on my ability.
There are styles more often faked (for example, 3 or 5 stone Victorian bands, Gypsy rings, Victorian solitaire colored stone rings with halo of diamonds, engraved wedding bands) because the style is popular/back in demand and the workmanship and raw material needed to do so is not astronomical. So I’m especially wary of these popular styles whenever they come up for sale, and have seen some truly abysmal ones where I seriously doubt they were put together by a primate with thumbs, never mind being antiques.
But at the end of the day, sometimes playing the wheel of fortune (given the price is not prohibitive) does have its own thrill too...Everyone loves the fantasy of having scored a deal, nothing wrong with that! Sometimes I’ve wondered too myself if it’s better not to ask too many questions in fear of bursting the fantasy.
In summary, if it’s a piece you love aesthetically and didn’t break the bank, I would just enjoy it and not worry too much, because there is no way of authenticating most antique pieces (as well meaning as we on PS try to help each other anyway!) short of taking it to a seasoned expert, and many “experts” are baloney anyway (it’s like the blind leading the blind).