Start with lean by identifying a specific problem to solve — preferably one that has a serious impact on the company’s ability to serve its customers. One company I know that has made incredible strides started its journey with the president (upon seeing their D/C filled to the ceiling with unshipped goods), setting a corporate goal for same-day shipment of orders.
Once a problem has been identified, I believe that introducing the A3 as a tool to solve that problem is a great way to start. Doing an A3 correctly necessitates going to the gemba; engaging in conversation; showing respect; and engaging in PDSA. If other tools are needed along the way, they can be introduced in the context of solving that particular problem.