Step 1> Make a stencil. I used some plastic sheets that used to be used for overhead projectors (if you remember those!). I made a row of holes with a hole cutter.
Step 2> base coat your model. On this I used Auto Air Aluminum base, but pick your own color.
Step 3> The key to getting a 3D effect is to put down some black. Here I uses AA Transparent black. I also added some gills so I knew where to start my scales.
Step 4> Place your stencil and start painting. I like Tamaya paints for this because you can thin them with isopropanol and they dry almost instantly. Here I an using white so they show up well. Paint only half of the circle. Remove the stencil and dry with a blow dryer.
Step 5> Off set the stencil and paint the next row until you do the entire side. Repeat on the other side.
Step 6 > When you finish both sides, go back and fill in any gaps and dress them up a bit as needed. Here, I painted some small scales on the head, darkened the back with some black, and touched up around the gills and eyes.
Step 7> Spray with transparent color, OR add a few light washes of diluted acrylic paint, dry completely, then seal with clear sealer.