"Effective writing has a purpose and keeps the audience in mind throughout the piece. Your tone and the way you write should always be appropriate to the purpose.
Purpose refers to WHY you are writing. It is your intention. What is it that you want to accomplish by writing this piece? Some of the most common purposes to writing include:
It is important to match your purpose to an appropriate form of writing. For example, if your purpose is to present information about Humpback Whales, you would probably choose a report format rather than a Limerick poem form. Sometimes there can be more than one purpose to a piece of writing. You might want to write a story that is amusing for people to read, but that also shares your feelings about stray cats.
The audience is who you are writing this piece for. You need to consider who the audience is because that could have an effect on how you write your piece. If you are writing a folktale to amuse small children, you would use different language than if you were writing a report for a scientist.
Part of writing in a way that is appropriate to the audience has to do with using the correct tone. Tone is the author's attitude communicated to the audience. Suppose your parent says "I'd like to speak to you." You can tell from the tone of their voice, how they say those words, whether you are going to get in trouble