it's nice to have at least one of each of these types of necklaces! this will give you some great styling options.
#1 -- the long, rounded necklace
long lavender bead illusion necklace from loft
any similar necklace will do. these look great with almost any type of neckline, whether it's a v-neck, crewneck, scoopneck.. it's a little trickier with a collared shirt because of the collar sticking up a bit, but not impossible.
#2 -- the bib/statement necklace
resin colorblock necklace from j.crew
galina necklace from banana republic
statement necklaces are a really great way to give your plain outfit some interest! these kinds of necklaces go really well with collared shirts -- you can even try the trend where the necklace is worn over your buttoned up collared shirt if you like. they can also go well with v-necks, depending on the size/type of statement necklace.
#3 -- the long pendant necklace
marta pendant from lauren elan
agate pendant from american eagle
the pendant necklace is a wonderful way to express your personal style, since you have so many options in what type of charm/pendant hangs from the necklace, be it quirky, cute, or elegant. the long pendant goes especially well with v-necks, boatnecks, and scoopnecks. be careful when pairing it with a collared shirt, because the way collared shirts are shaped, and how it intersects with the chain might make the chain look unnatural and oddly shaped. i don't know if that makes sense, but try it and see if it does that for you or not. :)
those are the three main groups of necklaces that i've observed when i go shopping.. if i missed any, please let me know in the comments! and i'd love to know if these tips helped you also! :)
(all images from their respective websites, linked below each photo.)