I started by just doing more, like parking further out to get a few more steps of walking in. And track your progress somehow. This is critical if you are going to ramp up from being completely out of shape. *

* I was bedridden for 3.5 months. This was followed by getting out of breath if I walked to my kitchen or stood too long. I imagine you are in better shape than that. I now walk 2+ hours a day.