Acceptance of the way of things is key. Acceptance that everything changes, leaves fall off trees, people get old, fall apart and die. To dwell on what you can't change and fill your mind with anger, depression, anxiety, regret, jealousy or any number of other negative emotions is to ruin the time that you have here. Shut down your thoughts when they want to go dark on you. Count your blessings. Be in the present moment, enjoying as much as you can. Try to take care of your mind and body as best you can.