If you use a treadmill in your workout these quick tips can help you maximize your workout!

Tip 1, INCLINE!
Walking or running on an incline. Walking or running on an incline will get your heart pumping and increase your burned calories. Also, if you are not comfortable running yet or can't run long distances then walking on an incline will give you a similar cardiovascular workout at a much lower speed.
It will also help build better calve muscles and work other seldom used leg muscles.

Tip 2, CHANGE IT UP!
Most treadmills come with pre-programmed workouts that change speed and incline during your run or walk. Make good use of these and you will be sure to increase your calorie burning potential.

Tip 3, PUSH YOURSELF!
Don't follow the same routine day in and day out. It'll take much longer to increase your endurance. Run or walk your starting speed/distance for a week or two then when you are comfortable increase your speed and distance slightly. Keep repeating this process. Eventually it will take longer to become adjusted to high distances and speeds so don't get ahead of yourself.

Tip 4, TAKE IT OUTSIDE!
When you're comfortable running multiple miles, or even walking multiple miles, you should really take to nature to progress your workouts. Running on different surfaces and in varying temperatures will help build up your endurance.
I have an uncle who is in his 60's and runs marathons, one of the top in his age group in Europe. He says there's nothing like running outside (then again he runs with beautiful Mountains and back country of Slovenia surrounding him) and like he said, once it's in your blood you'll never stop running.
So when you feel comfortable, get outside and run through a park or your neighborhood.