There are a lot of tricks to getting crisp lines. I use automotive paint because it flashes very fast. Generally I mist a first coat on to seal the edges, and then come back and hit it a bit harder for a few passes. Wait 20 mins or so and remove the stencils, and that is the result I get. Having a vinyl plotter also helps because if I have a problem area, I can just cut another stencil and reapply it.