I’ve read to build running stamina gradually, but is it possible to get results quicker by running more?
This depends how much and how often you run at the moment, and what your goals are.
The best way to increase your stamina is to do it gradually, though this is nothing to do with the stamina itself but more to do with your muscles and joints failing – injuries. If you can do several sports such as running, and cycling or swimming as well (these 3 compliment each other well) then this is a good way to go, the exercise can help you build stamina as well as being easier on your body.
However with cross training you still should only really increase your running miles slowly so your muscles can adapt. The 10% figure people quote is a good level for most people – low enough to avoid injuries and you can push it. If you do push how far you run then you have to listen to your body and be prepared to ease off if you feel that something is not right