Set a specific time for when you want to walk and when you should come back indoors. I do it all the time and it is quite effective in my opinion. I go outside at 6 p.m for some fresh air and then go back indoors at 7 p.m to relax and resume what I was doing beforehand.
Link your walking with any other work. Like watering plants in your terrace or garden, buying groceries and other stuffs from nearby stores by walking, etc. You'll never know you're rewarding yourself by doing a simple work. Then it'll be your habit that you won't feel ok if you don't go out for doing those stuffs.Also you can use smart trackers and fitness bands and watches to track your steps. You'll improve on the go. Don't expect results earliest. Your mind will do the rest just try to link walking with other work.
To stay well, walk for 30 to 45 minutes nearly every day. Do it all at once or in chunks as short as five to 10 minutes. Aim for a brisk pace of three to four miles an hour, but remember that you'll get plenty of benefit from strolling at a slower pace as long as you stick with it.