Witchipedia

FIRST you need to know that not everyone "see"s energy. Some people sense it in other ways. Personally, I feel it. I can see auras, but not nearly as clearly as other people report to and I have to really concentrate. The easiest way for me to see an aura is to look at the sky just above a group of trees, so you're half looking at the sky, and half the trees. I can see plant auras much better than people auras, but I feel it much better than see it and I kind of hear it too. (My eyesight sucks in general though.) But I don't really have a lot of use for seeing auras, so if I put more work into it, I might do better.

To see auras, I sort of have to look past a person. It's kind of hard to explain, but I took Karate as a kid and they taught us how to break boards. If you aimed for the board it would hurt like hell and the board would remain intact. If you want to break a board (and not your hand) you have to aim for the other side of the board, not the board itself. Seeing auras is kind of like that for me. If I look right at the person, I just see the physical, I have to aim behind them (sort of) to see the energy field.

I am not sure if my inexpert advice is at all helpful, but I hope someone else who knows more will jump in.

One way to practice:
Have someone stand in front of a white surface in a dim room. Candle light would work. And gaze around them. Don't stare, blink when needed. As already stated don't look directly at the area where you would expect to see it. (Shines the bightest around head and shoulders) Most who see it for the first time see it in their peripheral vision.

Auras
Merry meet to those who read this
Even if you are talking to someone, clear your head the best you can. Look past them. Envision their heart pumping.match it to your own.Concentrate on their movements,their eyes. just breathe, If you are talking, talk but try not to overthink anything.As you are slowly distracted,a glowing light (faint) should slowly appear,slightly. As you get better at syncing yourself with others it will become more natural. Therefore the better you are and the quicker you do it- the stronger it seems. It is best to practice in a public place, but one where you wont stand out too much eg. a coffee shop in a mall.
Blessed be, may the goddess aid you
Aithne

I have found that after practicing Kundalini Yoga for years that it has significantly increased my empathetic awareness.
It involves a lot of meditation and self awareness first.
I highly recommend Kundalini as a supplement to all magic. It helps you quiet your mind so you can put all of your focus and attention on the matter at hand.
I feel people more than actually "see" a color, but the feelings are linked strongly in my mind with colors. Don't worry about seeing colors, just try feeling the energies of a person.