Here are a few tips I haven't seen so far and I see a whole bunch of people at the gym make these mistakes:
-Don't move your shoulders. By this I mean, don't rotate your body with every step. If you swing your shoulders with every step, you waste all this energy when you could be using it to go forward. Swing your arms forward and back instead. I find, if I hold my elbows at 90 degree angles, I am more inclined to move my arms more and twist less. The people who hold their arms towards their body more seem to twist more.
-Don't make a lot of noise. If you are stomping away and making a lot of noise, unless yer a really big fella, you're doing something wrong and wasting energy vertically. A loud footstep means your feet are hitting the ground the wrong way with your feet.
-Don't run sloppy. If you get tired, maintain your form. When you run sloppy, you put more strain on your bones rather than your muscles. Your shins and knees aren't designed for stress without your muscles backing the weight.
-Breath at an irregular pattern. For example, breath in 2 steps, breath out in 3 steps. If you do this, you will breath on alternating steps and won't strain one leg. This really applies if you run really long distances but hey, I do it just because it helps against injury.
You said you had some knee problems. If I were you, I would find another thing to do. Running is really tolling to the knees and shins especially when you don't do it right. Also, one more tip I have is try to run based on time and pace rather than distance. What good is reaching your goal of X miles when you're crawling to the end damaging your body? After all if you're doing this for cardiac reasons, its better. My first runs started with 5 minutes out and 5 minutes back and a year later I'm up to 60 minute runs three times a week. I still run slow though.
Oh, I find it funny that most people are mentioning shoes as the first thing. Advertising executives at Nike and New Balance and patting each other on the backs right now.