The secret to a great headshot
100%- it's the expression! Yes, lighting and the right lens is important, but getting the expression you need out of your subject is the number one priority- and that's why you get paid the big bucks right?
A great headshot only comes when your subject is relaxed. That might take one minute, or it might take twenty. It depends on the person you're photographing, and your ability to make them feel at ease in front of your camera.
Things to consider with headshots is, firstly, what type of headshot you want to take. Is a corporate image, a picture for their business, or just a fun thing for social media? And are you going to be inside or outside? The ability to work with light is important, and light is infinitely more controllable in a studio, but you do not have to be in one to get a great result.
I personally prefer plain, non-distracting backgrounds (doesn't have to be pure white or black)- that way, you can shoot with narrower apertures (f8-10) and get the whole face in focus. If you're an outdoor shooter, be careful that you don't have things sticking out of your subject's head (like trees and poles).
Lighting for headshots is an essential technique to learn. Natural light is great, but you have better control if you use artificial lighting, be in flash or LED. I would avoid on-camera flash for headshots as the lighting is not going to be flattering, and you'll get a lot of unwanted shadows. The use of reflectors will also help get light into the right places. There are even more advanced techniques which will allow you to turn a mixed background into pure black or white in post-processing.
When you should headshots, you don't need fast lenses. I would not normally shoot this type of image wide open, so f1.4 is not necessary. This will reduce both the weight and the cost of your lenses. Tripods are great because they allow you to be free to have more interactions with your subject, but it's perfectly fine to hold your camera too. My preferred focal length is 85mm, but anything about 70mm usually gives good results. It allows you to stand back far enough so that you don't get any distortions on the face.
If you are able to do a little bit of post-processing (ie. editing), you can remove blemishes, stray hairs, etc. But it is preferable to get things as right as possible before you press the shutter- this will save you a lot of time. For example, headshots are often done in an office. If you're not using your own backdrop, you might run into background objects like power points, cables, clocks, etc. Don't make the assumption that these will be easy to remove later- depending on the background, it maybe quite time consuming.
So in summary, headshots are fun to do. They take some practise, and you will end up taking 50 frames to get the one perfect shot, but it's worth it. See you next time!