The American College of Sports Medicine has recently announced that adults should exercise at least 150 minutes per week (about 1.5%). The exercise can be spread out over the week and can be done in small increments each time.
Of course, they have considered that most people can't just jump right into an exercise regimen. The ACSM recommends planning the time each week so that you have time allotted for just exercising. Reading up on the benefits will help you realize the importance of being active.
Choosing a set time of day to do the exercise will help you develop a routine. For example, you can go for a brisk walk on your lunch break. This will not only help break up the day, but will expose you to the sun, which is important for vitamin D intake. Just remember to wear sunscreen!
After a few months, be sure to really think about your new lifestyle changes and how they are benefitting you. This is a good time to implement new things if you're becoming bored. A healthier you is a happier you, and who wouldn't want that?