Your body is yours only. Once you realize it, your motivation to keep it in best shape possible will increase.
You need your body to function well for many years to come. You see old people around you, many of them are not well, have illnesses, sometimes can't live normal life without support of medicine, other people or machines. When we are young we think about here and now and we forget to take care of the us. It is ok, young body has more abilities to survive what we put it through (bad food, lack of rest, addictions). But we get older with every single day and we don't know when the moment will come that the body will simply start failing and refusing to handle what we put it through. That is why it is important to start early taking care of ourselves.
Start with improving your eating habits - eat a lot of various vegetables and fruits, avoid processed food, avoid fast food, drink a lot of water. If you are overweight, control portions and quality of the food you eat. If you don't know which foods to eat to get healthier, ask your personal trainer or visit dietitian to look for help.
Be active and exercise regularly - find some form of exercises that you enjoy and can stick to it - it could be daily walking, dancing, Zumba, yoga, swimming, running, cycling, lifting weights, crossfit. Don't be afraid to try new things - all of us started somewhere and no one was born good at everything. Look for personal trainer if you are worried about your condition and lack of knowledge about what to do to get and keep fit. Coach can help you with your first steps in fitness.
Give your body enough rest and sleep - don't push it too far without adequate recovery time, as it will simply fail and you will defeat your goal of taking care of it. That is what most of people who want to get fit, lose weight or perform often forget. Sleep is as important as correct food and exercise. It is during the sleep that the body does all the necessary repairs in your body to keep it in best shape. So give it enough opportunity to do this job.
Work on your stress level - it is not easy at all nowadays, where we all try to organize our busy lives, earn money, take care of family, develop careers, face daily challenges. But this is what life is about, overcoming the challenges, planning, improving your life conditions step by step. When we stress our body produces hormone called cortisol which in excess negatively affects our performance and our health. If you are going through really difficult time in your life, look for help from someone, try to make a plan how to come out of this bad time, make small goals and be satisfied when achieving them.