Visualize your dreams. Keep visualizing your dreams and believe that you will achieve them
Be realistic. Make resolutions and set goals that you feel you can achieve
Be thankful. Be thankful for all the blessings you have
Be young at heart. Don't give in to your age -- keep active and exercise regularly; you will live a longer, healthier life
Enjoy yourself!  Choose an exercise you enjoy! Find something you like, and you will probably stick with it
Give yourself a reward. Pick a reward to treat yourself with once you meet your goal. Plan short term goals that measure your short term achievements 
Have fun. Keep yourself from getting bored by varying your routine, or alternating the kind of exercise you do
Keep a journal. Logging your activities (try it here) will help you achieve your goals
Keep positive people in your life. Look for ways to eliminate or limit the time you spend interacting with people who are negative.