My first attempts at using a gelli plate were, uhmm, less than successful. However, I continued to practice (and then teach) this technique and really like the results. The basic idea is to apply paint to a gelli plate, then use a variety of tools to add designs and textures before adding the paint to a page.
I used this technique to create backgrounds for several pages in my worship journal.
I taught this technique at a workshop earlier this summer. Here's a look at some of the designs created by participants in that workshop.