On especially busy days, you may not be able to spontaneously get a minimal amount of physical activity, so you need to plan ahead. Pencil in an exercise appointment, and consider it a mandatory meeting. If circumstances prevent you from doing everything you planned for the day, do what you can and don't worry about it. Tomorrow is a new day with new opportunities to exercise. If you fall off your routine for a time because of injury or illness, just get back on.
Interruptions are part of life.
Don't focus on exercises you find unpleasant or uncomfortable. Choosing activities you enjoy will help you stick with your program. Spontaneous exercise may depend on having walking shoes or a change of clothes available. Have equipment on hand. Buy a piece of exercise equipment, place it in a convenient location at home, and jump on it when you have a few minutes to spare.