The art of effective speaking can be learnt from the way the Prophet (sallallahu alaihi wa sallam).
MODERATE
The speech should be of a moderate duration. Some people came to Ibn Mas’ud (radhiallahu anhu) to listen to a talk. He did not come out of his house. Eventually they informed him. He came out and told them that he knew they were there but he did not wish to bore them as the Prophet (sallallahu alaihi wa sallam) would be considerate in giving them a lecture fearing that it might be boring for his Companions (Muslim 2821).
LEVELS
Speak according to the intellect of the listener. The Prophet (sallallahu alaihi wa sallam) said: Treat people according to their individual status (Abu Dawood).
Content should be according to the need of the time and audience. The Prophet (sallallahu alaihi wa sallam) was asked on many occassions as to what was the most virtuous deed and he gave different answers according to the need.
QUESTIONS
Ask the listener questions to get his attention. The Prophet (sallallahu alaihi wa sallam) posed questions to his Companions.
Use examples. The Prophet (sallallahu alaihi wa sallam) compared a Muslim who recites the Qur’aan to a citron fruit which is good in taste and smell; the Muslim who doesn’t recite to a date which has a good taste but no smell; a corrupt person who recites the Qur’aan to Rayhana (an aromatic plant) which smells good but is bitter in taste (Bukhari 7121).
DRAWING
Explain difficult matters with illustration. The Prophet (sallallahu alaihi wa sallam) would at times clarify matters by drawing on the ground (Bukhari).
Use hand gestures. The Prophet (sallallahu alaihi wa sallam) said: A believer to another believer is like a building whose different parts support each other, and he interlaced his fingers while saying that (Bukhari 2314).
These are tips from the Sunnah on effective speaking.