About a year ago, my wife and I started going for a walk once or twice a week. After a few weeks, we tried to run "just a little." At first, we would pick a mail box maybe 100 meters away and we'd run to it. Then we'd have to walk for several hundred meters before trying again. After four or five times of doing that, we just wouldn't run any more. I'd be winded by the time we were done with our walks.
A couple of weeks ago, I ran a half-marathon.
13.1 miles (21 Km) of pure run. It was fantastic. I'm going to run my first full marathon this fall.
There is no great secret to running. Just run until it sucks, and then keep running.
Get up the next day an do it again, only further.
I have some pretty significant lower body injuries that have kept me from running for years. I found out that by doing a little reading on what good running form is, and then concentrating on actually doing it, it put a lot less strain on my body. I also found out that the shoes all the 'experts' recommend to correct the gait problems inherent in my injuries actually made things worse. Now I wear shoes that don't try to force my feet into unnatural positions and I accept that I have a different foot strike with each foot. I've also learned to pay attention to my body and learn the difference between "this sucks" and "this hurts!". If it sucks, keep going. Sucks is good. Running through what sucks is what makes you better. When it really and truly hurts, I stop running. In fact, five days before my half marathon, I ran less than two miles because I was in pain and didn't want to risk aggravating injuries. I rested, I iced, and when it was time to run for real, I felt great.
As kind of a "born again" runner (I ran a lot through the 90s, but quit when I got hurt), I hope that everyone gets off their butt and hits the street once in awhile. No matter how slow you're going, you're still kicking the ass of everyone who is sitting on the couch. Stick with it!