One more thing which is extremely important is that you should get your form correct before you move forward. It can be wrong to move forward with the wrong form as this will take you nowhere. It will just pull you back and also increase the risk of you suffering from injuries.
When you want to become a marathon runner, there are few things which you should keep in mind. You should always remember that your hands should not cross your body. You should ensure that your hands are always around your hips. This is because if you keep your arms up your heart will have to increase the blood flow to it. This will increase your heart rate and thus pull you back.
It is also important that you put your feet at the correct place and in the correct form. You have to make sure that you do not stress your leg, knee, lip, and back.