1. Stop worrying about technique. Set up your lights before your subject gets to the studio, test them, test them again and then let it go.
2. Spend some time letting everyone get settled in. Don't feel like you have to rush through a portrait session. If you are doing it for money you're obligated to do a good job and that means slowing down and doing it right. If you are doing for the satisfaction then make the session like a lollipop. Lick it slowly instead of biting right in and chewing it all up. When you feel rushed it's hard to feel relaxed. Don't do rush yourself. My good sessions take at least an hour...
3. Do your own style. If you are trying to shoot the exciting "flavor of the week" style you are already doomed to mediocrity.
4. Don't be afraid to fail. But don't be afraid to succeed either. You can't force someone to have a good day but you can be relaxed and empower them to have a better day because they are in front of you. Experiment with extending and improving your own style. Experiment hard with your listening.
5. Really talk to your portrait subject. Not just generic chit chat from behind the camera but real stuff. Ask what they love. Do they have kids? What do they do for fun and fitness? Share feelings.
6. Use a longer lens. There really is an optimum focal range for a flattering portrait. Too long and faces look one dimensional and smushy. Too short and noses get bigger while ears get smaller. If you are shooting a classic headshot portrait with anything shorter than a 50mm on full frame you're just being mean. Conversely, if you can't have a normal conversation with your subject because of the distance between you then you are being too skittish. Be less like a scared rabbit and more like a best friend. 100mm on a full frame camera makes me and my subjects happy.
7. It's easier to compose well in a square. Try it. No reason to be captive to the dreaded 3:2.
8. If you are shooting portraits for pure recreation/art/hobby/happiness then never photograph anyone to whom you have no attraction whatsoever. Just having a warm body in front of you is not enough. You must be interested to find out more about the person. In a sense taking a portrait is just a pretense to find out more about the person in front of the camera.
9. If you want to see beautiful people in your final images then you'll have to start by either finding obviously beautiful people to put in front of your camera or.....find the beauty in the person and put that in front of your camera. Warm bodies for "practice" is not enough.
10. The best way to become good at taking portraits is to do it over and over again. It's like any other pursuit in life. Practice makes fluid. When you've been through all the permutations of Murphy's law, both physcially and mentally, you start down the path of figuring out solutions to anything that might hamper your highest and best portrait expression. To love portraits......shoot more portraits.
Bonus tip: Everyone looks better in black and white....