To someone who's never lived in my house they'd think I have an ordinary back yard.
Someone who's never lived in my house might think I have an ordinary back yard.--- I fixed the sentence, but really... this intro sentence is meaningless. Why would anyone who has never lived in your house presume to know anything about the yard?
This is the way to begin:
My back yard is like a book where every page has a different story to tell and every sentence a happy memory.---- now this is a great sentence!!!!!!
I'll change it a little:
My back yard is like a book in which every page has a different story to tell and every sentence a happy memory.
That is the way to begin an essay!
As for the title, you have to choose one on your own!! :-)
Description like this needs more imagery words -- not just colors and images, but also sounds, smells, textures, etc. Add words that activate the reader's imagination.
Your conclusion, intro, and title all need to express the main idea. What is the insight you are sharing here? I know what it is, and you do too, for sure. Just come up with a clever 1.) phrase (title) 2.) sentence (thesis) and 3.) paragraph (conclusion) to express that main truth about the significance of one's place for memory making.