First, let's get rid of a few myths...
- stretching does not prevent injuries
- if you run less than 45-60 mins, you don't need to worry about dehydration
- fat gets burned as soon as you start running, there is no minimum amount of time you have to go running before that happens
That said, here's my advice (in case you might be wondering, I used to be an amateur track athlete until like 15 years ago, but still do running as a regular routine since then; and I'm fit despite drinking and smoking and eating lots of nice stuff

):
- go running at least two times a week, better three times, with at least a day for recovery in between
- don't force yourself at the start too much, it will result in injury
- set yourself a distance you want to run; starting with about 3 to 4 kms is enough, once you can run through them at a decent speed (like, 15-20 mins), increase the distance
- keep a steady speed, don't slow down; if you're exausted and can't continue running, then start walking for a few hundreds meters to regain breath, then continue running;
fast walking is better than slow running, both for your muscles/joints and for fat-burning!
- try to avoid tarmac or other hard surfaces
- buy good shoes (good meaning: they fit your type of running; go to a pro store to find out more), and change them every year
- stretch, but don't force it
Most important for reducing weight and burning fat: Move.Move.Move. Running alone won't do the job, that's a painful truth. You need to move your ass whenever possible. Take the stairs instead of the elevator. Get out of the bus one stop before, and briskly walk from there. Or use a bike. And: reduce fat and sugar in your diet! Eat protein and carb-rich food.
Getting in shape is a great experience, have fun!