This is an often asked question. There is no definitive answer to this question. Alot depends on where your business currently is situated. Ideally, lean should be implemented as part of an overall business plan. In fact if your business hasn't already developed a lean business strategy then what are you waiting for!
A lean business strategy is a roadmap to your desired lean outcome. Like a business plan, a lean business strategy includes a gap analysis of where you currently are compared to your desired state. Then step by step activities are developed to enable your business to progress towards a lean business.
Without a lean business strategy you may achieve initial results as you pick from the low hanging fruit, however, once these easy problems have been fixed it will not be clear which direction you should follow next. A lean business strategy will provide these steps to ensure you do not lose momentum or focus.
So, where should you begin? By devoloping a lean business strategy of course!Once you have developed your lean business strategy you will know where you can begin. 7 Steps to a Lean Business details the pro's and con's of the 3 choices - Start at the end; Start at the beginning; Start at the bottleneck. Each of these choices will help your business, some more than others.
Where ever you choose to start, the most important thing is to start. The biggest failing in lean implementation is when people wait for the right time - that time is now.