Just try different things! I like to lay my rod on the ground (obviously watch for sand in the reel, so if anything keep the handle side facing down), and lay the fish against it 'sitting up' if you will. Or try lay it against different textures (reeds,sand,a fallen log, side of the kayak, boat etc) and different angles. Get close to the fish, or close to the ground. Take a release shot if you're keen, nice and close to the water (just don't drop your phone!).
One thing to make sure of though, is always keep the fish's head in focus!
Here's one i took with my crappy Nexus 5 phone camera, with a little editing:
Nothing amazing but hopefully the advice is of some use to you!