It depends on the level of your running experience, age and motivation. From my own experience, don't overdo it otherwise you won't keep it up. Try and improve slowly and steadily. Read my post about how I got into it here.

There are a lot of factors that will influence your abilities and runs, so if you need more advice please ask. What helped me personally (I was 36 when I started), start with walking and build it up, going further then faster, then start jogging/running. Set yourself small goals, 1km without stopping, then 2km, then 4 km until you are at a satisfactory level.

Once you've reached that level, search for varieties in the course, otherwise it might get boring. Add declines and inclines.

I hope this helps, this is off course based on personal circumstances and they can differ to your own.