Fishnets have a bad reputation as something that is "trashy" or can only be worn when you're trying to look edgy or dark. This really sucks, because the fishnet composition of fishnet tights means you can attach almost anything to them. One of my favorite compositions are fake flowers and craft pearls. I recommend just gluing the pearls and fake flowers to the fishnets. Getting fishnets irreparably dirty is pretty rare, and if you do, they're usually ruined enough anyway that you can't wash them, regardless if you've added any clunky attachments.
The best way to do this is with thin wire and glue. Dab the wires with glue, adding a flower of pearl to each. Make sure the glue is set before carefully winding the wire around part of the fishnet, insuring that everything is tight. If the flower of pearls is sagging, tighten the wire up before snipping off the excess. Make sure it's craft wire. That way it doesn't irritate your skin. You can go off the graphic above as a reference, or make your own flower and pearl composition.
If you have fun with this little craft, then feel free to do more cool fishnet crafts. They can be way more versatile than you think!