A portrait is the best way to save someone's essence in that point of his or her life. I believe it is something very intimate and that's why I suggest you start with someone you know.
The best portraits of modern photography history are normally these amazing productions where everything is extremely planned and the results are breathtaking. What can you do when you have no clue on how to take a portrait? How do you place your subject? What do you ask him or her to do? What should they wear? Where should you do it? Smile or no smile?
Now think: if this is stressful for you, can you imagine what the person in front of your camera is feeling? Truth be told, this is very intimidating. So now, stop and think what could make this whole process easier and more enjoyable for the both of you.
My first tip is to choose well your first victim (or subject, but victim is funnier). Try to pick someone you know, someone you like hanging around with. This will make everything flow much, much better and you’ll both feel way more comfortable. Chat with them beforehand and explain what’s on your mind and what you’re trying to accomplish with your portrait shots. Sit down and have a beer. Trust me, it works like a charm. Especially if it’s on you ;)
Before you sit (or place or whatever you like) your subject in front of your camera, talk a bit with anything that’s not related to the photos you’re about to do. This will help you break the ice A LOT. If you are able to make them laugh, even better! this will give you a great thing to shoot. Once the atmosphere is easy going, start taking your favorite Lomography camera out, as fast as you can almost ninja style and start shooting.
After a few shots, you’ll be both comfortable with the process and it’s now time for you to look into the details. Do you like the background? The way he’s standing? The hair?. Step back and take a minute to analyse all the little things. I suggest to start it off with a clean and flat background with little to no texture, and if it’s just one color, even better!
Think about the fact that your subject has absolutely no idea of what your shooting, so help him/her a bit. Look through your camera’s viewfinder for a composition in your portrait. Do you want just the face? Full body? Maybe in the middle of a specific atmosphere? Once you decide, try to explain this. How you want them to move their bodies, their face, either looking to the camera, or not. It all depends on what you’re looking for. I just ask you to keep something in consideration. please, please, please don’t ask them to smile, that will definitely make them way more nervous.
One last thing, in my case I love using black and white film for portraits. I’m a huge fan of the results. You do lose that color explosion from your x-pro shots but you win so much definition on those monochrome ranges. ;)