If you’re going to effectively communicate anything, you have to be able to step back and evaluate your communication. When you’re communicating visually, that means you need to step back and see the whole picture.
The selfie has been demonized because we all take so many of them to share with our friends, but it’s a great wardrobe evaluation tool. You don’t have to share the selfie to use it, and even a full length mirror won’t tell you as much about the effect of your outfit and your use of proportion as will a quick picture. I can’t tell you the number of times I took a picture of an outfit and changed it, even though I’d checked myself in the mirror.
But you do need a mirror. And, if you can manage it, you need a mirror that you can use to see the back of your head, if you ever wear your hair up, and a mirror that you can use to check out your profile. More people see you from the back or side than see you straight on, so the trick of angling one mirror to see the reflection of a mirror set opposite is quite useful.
Remember that when we look into the mirror, we focus on the features that we love and hate the most rather than the overall effect, and when we look at a picture, we see the person within as something of a stranger. They’re both useful tools, and I urge you to use them both when evaluating your effect on the world at large.