Consider the vibe you are going for. Sometimes I wear two delicates together, but I never wear two statement pieces together. Yes, they are relatively small, but they are in the direct line of vision of anyone you talk to, so they should be well considered.
The first thing to look at is whether the necklace style is right for your body. Though cross necklaces have been around since the Roman Empire was Christianized, recently, crucifixes have become popular tropes among jewelers like New Top Jewelry and Instagram-popular brands like Bagatiba and Vanessa Mooney for fashion's sake.
Inexpensive, stylish and in a range of sizes and designs they make for good layering options with your more expensive pieces or as an entry point if you just want to dip your toes in the trend.
So, leave the rest of your look toned down. A more modern look is to layer a few necklaces with a v-neckline. This pink ruffle neck sweater is a situation in which a necklace is optional, in my opinion.
There are endless varieties of pendant necklaces in stores right now, from eye-catching unique styles to simple, delicate ones.
Also, this is an example of two pieces that are more equal in visual weight — both delicates, and pair well together.
The matching shades are a nice touch, no?