Lead by example, rather than by instruction.
This may be one of the "golden laws," but the iron law behind it is that you are always instructing by example, even (or perhaps especially) when you think you are instructing by precept. Preaching from the text may or may not teach the text, but it always teaches preaching.
I would say Lead by example by following your own instructions. Instruction is still necessary (and more important than example). The world is not watching your every action, waiting to emulate you. If you want someone to learn something new, you must tell him. If you don't practice what you preach, you lessen the effectiveness of your message. If you don't preach what you practice, it is unlikely anyone will ever notice.
I should say that the above risks overlooking the peculiar strength of the implicit -- the basis of the observation that "culture is invisible." The nature of childrearing is a case in point: vastly more is learned by the child from by observation, and probably still more by the sharing of stories, than by any amount of preaching.
I recall, about twenty years ago in a U.S. West Coast telecommunications firm, a sudden and somewhat obsessive preoccupation with "corporate culture" -- followed by some exceedingly ill-advised and ultimately ludicrous attempts at "cultural engineering" -- the attempt to exert explicit control over the implicit. The results convinced me that the prime movers had no idea at all what a culture is, let alone what culture they had. When posters about "Our Values" come into conflict with a purely narrative or observational sense of culture, the posters become unseen long before they are no longer there to be seen.
A field ethnologist I knew years ago told me of something he observed among the Gururumba of the New Guinea highlands. Every day about midmorning, a group of four or five elderly men were to be found sitting outside the doorway of one of the village huts. They sat in silence together for anywhere from an hour to ninety minutes, and then, as one, they would stand up, dust themselves off, and go about their several businesses. Each, when asked, could give a cogent account of why these "meetings" took place. What he got instead was a sheaf of very fine stories, no two alike -- and he did not believe there was any intent to mislead him. It was rather that transmission of this particular behavior relied on observation and mythological narrative rather than on prescription or explanation. He suspected that there was some richness in the practice, but that his own conceptual map was too far "off" to get it.
Instruction is still necessary (and more important than example).
I disagree. People misinterpret instructions so easily, and that's when they're receptive to them in the first place. I find that leading by example is just as important, and possibly even more so. People have a natural tendency to imitate those they respect. Watch for it... you'll see it! Looking for signs of people unconsciously imitating you (your speech patterns, your colloquialisms) is also a way to judge what people think of you.
In my opinion it depends on the organization we are talking about. There are organizations where participation of individuals and intellectual contribution is an important asset, so in these cases just "Preaching Leadership" without a direct involving means is just demagogy.
Unfortunately, there are others where the environment needs, or promotes, low level of participation and involvement. So there are 2 main types of workers => The "thinkers" <= with high level of responsibility ( no dirty hands ) and the "doers" <= with low level of responsibility ( those that "do the work" ).
See: ActInsteadOfComplain DoAsiDo