1. To provide guidance or leadership through some means or manner. As a parent, I always try to lead by example. The new CEO of the company has chosen to lead by force, dictating the terms by which his employees are expected to operate.
2. To provide someone with guidance or leadership through some means or manner. In this usage, a noun or pronoun is used between "lead" and "by." I find that leading the students by example yields much better results than simply presenting information to them. You'll get a lot more out of your team if you lead by consent than by demanding what you want them to do.
3. To guide or direct someone, something, or an animal by grasping and pulling them by a particular part. In this usage, a noun or pronoun is used between "lead" and "by." He lead the child by the hand out of the burning building. I was leading the bull out of its pen by its nose ring when suddenly it got spooked and tossed me over the side of the fence with its horns.
4. To directly control, direct, or guide what someone does or how someone acts. In this usage, a noun or pronoun is used between "lead" and "by"; typically followed by "the nose" or "the hand." I can't stand the way your mother leads you around by the nose like that. Aren't you sick of her telling you what to do all the time? I hate having to lead new interns by the hand until they figure out how to do the job.
lead someone by something
to guide someone by grasping a part and moving. Do you expect me to lead you around by the hand, showing you everything to do in your job? The cop grabbed Max and led him around by the collar.