I cut out the shape I wanted out of heavy paper like an index card and glued about 3 layers together and punched holes around the outside rim with a small hole punch.
Next, I crocheted around the shape in the holes the pattern I wanted.
Then I found a small picture like flowers etc. and glued a few layers or paper to the picture that has been cut in the same shape as my crocheted pendant.
When those layers are dryed, I glued them onto the pendant. The back is covered with a layer of paper painted a color close to the crochet thread of the pendant and then placed Mod Podged over the front and back of the paper to seal it. If you want, you can also stiffen and seal the crocheted part.
After that, I crocheted a tight chain for the necklace,put on a clasp and a jump ring at the end with a bigger jump ring fastening to the top of the pendant to loop over the neck chain.
I sometimes glue a clay stone on the crocheted shape(and just paint it a color of my choice and seal it with a sealer like Mod Podge) or use glitter or gloss. I have also cut out a small picture and glued it on top of the clay stone and sealed.