I love to run. I wasn't always into long distance, but since learning to run 10k in my mid-20s I have enjoyed it ever since! It doesn't cost much (please don't go for the cheapest running shoes, choose the ones that fit your feet properly), you can do it anywhere, and it's very therapeutic.
Since being around runners, I have seen and heard many running strategies. If you are thinking of taking it up, a run-walk program is the best way to start.
But beware of the following:
Whoever tells you not to do resistance exercises when training for long distance running is WRONG.
Resistance training is an important part of an exercise program. Placing load on your muscles is what creates the science in our bodies to build strong bones and prevent osteoporosis (among many other things).
Since I have been in long distance running, I have heard too many times people say 'don't lift weights, it will make you heavy for running.' This is flat out WRONG. And in fact, setting you up for some potential problems.
There are 3 main areas in which strength training improves your running:
1) Reduce Injury
2) Improve Running Speed
3) Improve Running Economy
Well there is science to back this, scroll down to the bottom of Runners Connect article, I have also experienced it first hand.
I learned to run 10k using a 13 week run-walk program. A friend and I did it together. The only difference in our training - I was hitting the gym to lift weights 2 to 3 times per week and she was not. By the end of the 13 weeks, I could run faster and it felt like I was floating. Completely contradictory to those that claim strength training will weigh you down.
The same philosophy holds true for sport. I see lots of children and teenagers who are lacking cross training, and it is leading to injuries.