I really love the idea of layering up loads of jewellery to really put some oomph into an outfit. Bebe Zeva of Fated to be Hated does it particularly well!
Costume jewellery is particularly good for this because it tends to be bold, bright and rather affordable. Generally, with designer jewellery you’d want to have it on its own standing out. There’s no worries there with costume jewellery. Layer it up to turn heads!
Stackable rings are great to get that chunky look. They can either be separated out and worn across both hands or they can be stacked.
Necklaces can also be layered up. Try to stick with one colour or theme. Multiple black cross necklaces can give edge to a gothic-style look. Or using necklaces of different lengths can add interest to an otherwise plain top.

It’s the same with bracelets. If you have bare arms or are weating a simple long-sleeved top then a stack of bracelets could look fantastic.
There is, of course, the chance of over doing it. There’s no need to wear 12 necklaces and 32 bracelets. If you are going to stack up your accessories then maybe stick to one body part.
They also say never to mix gold and silver jewellery. I disagree, this discord can often work well. Especially if the colours help to tie different pieces of your outfit together.