Well first and foremost you should integrate some sort of fundamental cardio exercise into your daily routine.
If you like cycling, maybe do some moderately intense bike riding for 30-40 minutes a day. Running or jogging are good as well, as long as you don't have knee problems. I'm genetically predisposed to having knee issues, so low impact cardio exercises such as cycling are better for me.
Afterwards, you might want to integrate some form of strength training in order to promote muscular health. Any time I fall behind on my strength training routine, I like to pick it back up with some standard body weight exercises. A circuit of squats, push-ups, pull-ups, and abdominal crunches is a simple yet effective way of activating all your muscle groups.
Eventually you may get some equipment or a gym membership and do some weight training but a lot of people have gone very far with just body weight exercises.