A lot depends what you want to achieve from your training / running :
Slow running / jogging is fine for keeping your weight down and your general well being, but if you run at the same pace / same distance / same route / same time, every time you go out, your body almost goes into " neutral " and you don`t really achieve anything.
However if you mix it up a bit, putting some hills in and some sprints in, after a few of weeks you`ll notice that you`ve probably knocked a few minutes of your normal time, without even thinking about it, your running more comfortably and your recovery period afterwards lessens.
From what I`ve read, you shouldn`t try to do too much too soon, as you`ll injure yourself, as your body isn`t used to the new strain your putting it under.
If you`ve changed your training, you should allow six weeks between each step up.
Have a look at these running methods that you can incorporate into your routine :
Tempo Running.
Interval Running.
Cruise Intervals.
Fartlek ( Swedish )
Hill Sprints.
There are others, but they`re only really relative to competition running.
If you mix your running up, it also stops it becoming boring too, which is half the battle