I'm delighted to offer help here! There are these things called stereograms, or Magic Eye images that use the same unfocused convergence and divergence necessary to see auras. It is extremely relaxing and healthy for your eyes, and can even improve your vision over time. It is an exercise for your eyes. If you are in pain, you are more than certainly doing it way wrong!
I personally think of auras as more than just one thing that you are looking at. Like if you look at your physical body you see color and matter, otherwise colorblind folks would just be blind. I think it's radiant body heat, emf, magnetism, thoughts, and maybe a mixture with the negative color of our skin to create the color.
for viewing, I think other people are better subjects at first. Watching a teacher, preacher or other speaker while they speak with the relaxed unfocused gaze will not look weird and will give you tons of movement and thought expression to fluff out their aura for you.