In my opinion a lecture is one person telling another person he is stupid. That's my view on them. It's a method for a person who "knows more" or "thinks he knows more" telling another person what is right and what is wrong.
According to Dictionary.com I'm not far off, because the official definition is "a long, tedious reprimand."
A lecture must not be confused with educating. Educating is when you help someone become a better person, or to become better at a specific task. Educating is beneficial to both parties involved, and a lecture is never beneficial to anyone.
So it is my humble opinion that if someone does something that irritates you, or that you think is wrong, educate that person, but do not lecture. A lecture, especially the "long, tedious" type, can leave one or both parties feeling quite awkward.
In my view there are 2 types of lectures.
1. Educational lectures: one person educates another
2. Angry lectures: one person tells another what he did wrong
3. Teaching lectures: School or work and performed by professional
Teaching lectures are usually good. The other two are subject to complications. You are a mom and you don't want your son to grow up and have no respect for himself. So you give an educational lecture about not just dating someone out of convenience, or someone who has no respect for you.
This can be adventitious, yet given at the wrong time can simply make your son not want to hang around mom because "she lectures me all the time."
I cannot think of few examples where angry lecturing would be of any use, unless the situation you are lecturing about is life or death. For example, your daughter crossed the road in front of another car. Then you might get a little angry and scare the bejeezers out of the child.
Regardless, if you must perform an educational or angry lecture, follow these simple rules:
1. Don't do it
2. If you must, limit it to 30 seconds. If you can't make your point in 30 seconds, you won't.
3. Stay calm and don't raise your voice
4. Don't assume the other person is stupid.
5. Listen to the other person.
6. Work together with the other person to find a solution that works
7. Be patient
8. Educate instead (see rule #1)
9. Be aware there is more than one ways to skin a cat
10.Do it very seldom