 A metaphor is a comparison of two things  Remember that unlike a simile, a metaphor does NOT contain the word like or as  A metaphor says that one thing IS another

 So what is an extended metaphor then?  It builds upon a basic metaphor.  Two things are compared at some length and in several ways.  But you still follow the same rules as a metaphor.

My mum is a general. She stalks through the house telling me what to do. She then sleeps throughout the night. But when she wakes up..... her medals clanking, stars shining & roars us to attention she barks orders as she charges through the house: " Lisa, do the dishes ! " " Lisa, clean your room ! " then crawls back to her bedroom while we, her dutiful soldiers carry out her orders.

 What was the extended metaphor in this poem?  Notice how this metaphor ran through the entire work.  Another example is that in George Orwell’s Animal Farm, the farm is compared to a nation, with different possible forms of governance. This comparison extends throughout the novel.

Most of the time extended metaphors are implied. Instead of the author saying that their mum is a general, they might just imply it. What is implied here about the speaker’s love? Oh, my love has petals and sharp thorns. Oh, I placed my love into a long-stemmed vase And I bandaged my bleeding thumb. And here, what is implied about the city and the subway? The subway coursed through the arteries of the city.

But Avoid Mixed Metaphors (combining two or more incompatible images in a single figure of speech): Management extended an olive branch in an attempt to break some of the ice between the company and the workers. And just remember that like with any type of figurative language, there is such a thing as over- kill.