Start slow.....
In my own experience starting slow is the only way to go, even if, like in my case, it begins with just walking. I ran for the first time ever (when not being chased or forced) a couple weeks ago after years of thinking joggers were stupid idiots out to make me feel bad (they always look so damned content with themselves...). But I loved it. But of course, being 50-60 pounds overweight, I have to be realistic about it. My knees too have a history of unhappiness and at one point doctors reccomended a long and dreadfull series of surgeries. But luckily a nice physiotherapist saved me from that pain and anguish. She told me exercise would get rid of those problems better than any surgery, but i had to take it slow... And to her credit, it worked! never needed surgery and the problems dissapeared!
So recently I started walking again, slowly upping the distance and time till I was doing 10km a day. Once at that point, I tried little runs around a neighborhood park, sticking to the grass to avoid as much jarring impact as possible. Once again I took it slow and would rest frequently, though I would continue walking while resting. I can now run a solid 1.7 km lap around the park before needing a break, and can do it three times before falling down. Certainly no marathon and the breaks get more frequent as I go along, but it is a start. I often think to myself while I am doing it "OMG!!! My fat ass is running!!!" Whereas I wont win any races or impress those skinny little joggers, I feel like 10 million bucks! But it is all about pacing yourself and working your way up to it.
I told a large friend of mine about how good it made me feel, so he took the opposite route and went for a 5km run to make himself feel better. Or so he thought. He got 2 blocks from home, with no stretching or prior training(at 350+ pounds), and tore some muscles in his thigh pretty good, also taking a fall and twisting his ankle. Not only did he not make it the whole 5km, but he could not even walk home and had to get a cab to take him back the 2 blocks he had gone. Some time recovering on the couch while taking pain killers and now he has no interest in continuing working out period. "Running is stupid and not good for you" I believe were his exact words... A positive to a negative in a matter of 2 blocks.....
Preparation is the key. May sound silly, but as babies, we all have to start crawling before we can walk. The same applies to running. Someday I know I will be able to run a marathon, but for now, running, somewhat continuously for 30 minutes is a dream come true. if I had pushed it like my buddy, I may have done EXACTLY what he has done, and decided that running and exercise in general is not worth the effort.
And thats just way too bad....
sirant
