Learning to see an aura is more tricky than difficult. It isn't a skill you may or may not have. As far as I have been able to tell every human with functioning eyes can learn to see auras. I have been able to teach completely non-magical people to see auras. The only time I have ever found a hitch in my ability to teach this skill is when I was trying to teach someone who was colorblind. Even then he said he could see them but obviously was not able to interpret the colors as colors, having had no frame of reference. I'm still working on that problem. That being said there are a few things you need to know about auras before you learn to see them.
First and most importantly the colors in auras are not colors at all, they are wavelengths of energy that our brains interpret as colors. As such they have several properties that colors do not have. For starters, it is totally possible for an aura to be both red and green at the same time and in the same place. This can be difficult to see because our eyes are not accustomed to seeing these two colors at the same time.
Second, the colors don't always mix the same way. A green aura, for example, is NOT the result of a mixing of yellow and blue in an aura. Green is its own color separate and distinct from both yellow and blue.
Thirdly there are colors in auras that are very important in the color wheel that are not a part of a normal additive OR subtractive color wheel. Rose is one example of this, so are chartreuse, white and black, brown and silver. I will be going over the meanings of all these colors in turn in my aura color posts so please don't ask about colors in this thread.
Now on to learning to see them. First, we need to know what they look like. Auras don't specifically glow like a candle flame. They look more like sunspots, those little things you see on your vision when you look at a bright light then look at a blank surface. They also look vaguely like phosphenes. Phosphenes are those swirly glowy colors that you see when you press gently on your eyelids with your eyes closed. Okay, there are two ways I know of that work very well for seeing auras. The first way is the method I always use, it works easier for me. The second way is a way I can use if I am having trouble with a particularly complex aura to see more detail, but some other people have told me that the second method works better for them. You will have to try both and see what works for you.
First method: Front view; This is a way to see auras straight on. When you are looking for a front view of an aura, look at the subject (person typically but I have quite a bit of luck with photos as well as long as there's no color distortion), then try to find the darkest part of their image. On dark-haired people, this is usually their hair. For blonds or those with white hair, it is often best to find a shadow under their arm or chin. Lowering the lights helps with this quite a bit, just don't lower the light so much that you can't see. Now try to see the colors that overlay over the dark part of the person. The reason you are looking at the darkest part of the image is that those colors show up better against a dark background. It will be tricky at first, you have probably been training yourself to ignore these colors thinking they are a trick of your eyes. They aren't. They show up overlayed on the person's image just as sunspots are overlayed on your vision or phosphenes overlay on the blackness of your closed eyes. The benefit of the front view is that when you see the colors you will see them in large quantities for color comparison, giving you a very detailed idea of hue and saturation. There are several drawbacks to this method. The first is that colors lie on top of each other with this method giving you confusing jumbles of colors in auras with many distinct colors. The second is that colors like black and dark purple or blue do not show up as well against dark backgrounds as all the other colors. While black and dark blue and purple are rare colors they do exist and if you don't know how to look for them against a dark background you might miss them. Be sure if you use this method to look for other clues as to the presence of black. For example, if the shadows on a person seem too dark, that is a good clue they probably have some black in their aura. Also if their hair seems darker than it should be for what color it is, for example, a blond seeming to have dark hair despite it being fairly light blond.
Second method: Side view; This method works very well for other people. I confess it has never worked as well as the front view for me. Try both. The goal here is to see the aura from the side. Look at the subject's outline. This is the place where the edge of their form meets the background they are in front of. You will see a glow that looks like very thin layered colors literally between the subject and the background. The benefit of the side view is that you will see all the colors layered rather than stacked. This makes it easier to pick out distinct colors if there are two colors that are similar such as red and rose in the same aura. With the front view, red and rose often blend together, you will see them distinct in the side view. The drawback to this view is that you will only see a very very thin band of color. It is difficult to get an exact hue or a good idea of color saturation with such a small amount of color to see.
The last suggestion I have for now is once you learn how to see them practice it a lot. The more you practice the easier it gets. I had to concentrate hard when I first learned to see auras, but now it is quite easy. This happened because I practiced every day.