Focus on your core
Tighten your abs while you walk, but don't forget to keep breathing. You will soon notice how this works on your abs. Focus on your belly and keep the right posture.
Waling everyday is a great habit, but it might be difficult to walk more than 1 hour a day. If so, walk longer than usual on your days off. If you can walk with friends, it will keep you going longer without getting tired. Or walking in a big park or inside city is enjoyable, too.
Use walking poles
Have you seen people using walking poles? These walking poles can help you bur calories more and reduce the stress on the joints.