I am a gelli plate fiend. I love it in a way I don't love any of my other art equipment. You can't go wrong with it. Slap on some paint and you end up with some fabulous papers. If the overall paper looks a bit 'yuck' then crop it and cut it and play with it and you can still make something pretty. It's ideal for my beads and card making.
I recently discovered that you can use Indian print blocks to lift paint out layers of paint on the geli plate. You know - the wooden ones that are used for printing fabric. The ones that, if you are like me, you bought years ago and ended up being stuck in a drawer. They give an amazing effect. I tried the same technique with rubber stamps but the lifted image was not as clear as with the wood blocks.
All you need to do is roll your first layer of paint onto the gelli plate and make a base print. Let it dry - or dry it with a heat gun if you are impatient like me. This layer of paint will show through the gaps created by the wooden block so pick your colours carefully. Roll out your second layer of paint and press a wooden printing block gently into the surface of the paint to lift some of it off the plate. You don't want to really press hard and risk damaging the plate, just enough pressure to lift off the paint. Take your second print on top of the first and you should have a pretty pattern. Remember to clean your wooden printing blocks after too.