It is a common trend during late Autumn to start moving workouts indoors. Treadmills and spin classes are staples of Winter fitness. If layering up to brave the cold keeps you from running, then move your workout inside, but keep these tips in mind:

• Ease into your treadmill runs. Don't expect to run as fast or as long on a treadmill as you did outside. Allow your body to get used to the treadmill's movement and surface. Start with shorter, slower runs and gradually increase time and speed until you're up to the level you were doing outside. Running on a treadmill is truly a repetitive action, since the surface never changes, and this is another reason to ramp up slowly.
• Reconsider your sneaks. Trail runners were made for running outside on dirt paths and aren't exactly the best shoes for a treadmill or an indoor track surface. You may need to purchase another pair that's strictly for indoor use.

For other tips, .

• If running on a treadmill aggravates your knees, opt for using an elliptical instead.
• Remember that running on a treadmill with zero percent incline [1] can give you shin splints, so set your treadmill to at least one percent incline.
• Take advantage of the incline on the treadmill to simulate running up hills.
• Some folks think running on a treadmill is easier, so make it more difficult by varying your speed. This kind of interval training will not only work your heart and lungs and strengthen your muscles, but those sprinting bursts help to burn more calories [2].

Taking short breaks from training can be beneficial, but the longer you wait, the harder it will be to get back into the swing of things. If you own a treadmill or elliptical, dust it off, get it out of your basement, or remove the laundry you have hanging from it and start running. If you don't own one, join a gym immediately so you can use their equipment or indoor track.

Source [3]