Hello. I'm planning on Writing a book but, I'm not sure how to start... I already know I want it to be like Alice in Wonderland, the Wizard of Oz and the Narnia series, Where the main female character finds herself in another world, what I need help in right now is how does she get to the other world? My two options are, she falls into a coma like state where she dreams of her fantasy world, or should she find a secret passage? Any other suggestions would be most helpful!

I don't want to discourage you from writing, but these ideas have been used many times already. Better would be to take a small incident from your own life and create a story around it. For instance, I rescue stray cats. A mother cat with three kittens came to our front door to get food for her little family. I wrote a story about that cat family. I wrote and got published a story about an autistic boy I know. A Chinese friend wrote a story about her mother in China who made her children's shoes out of scraps of cloth. She also wrote a story about her mother's chicken that no one thought was laying eggs (but she was and hid them in an interesting place).

Write what you know. It will be much more charming and acceptable than if you try to copy the plot of a famous story.

I agree, it's very important to have original ideas. Don't just take bits out of other people's worlds and use those. Try to invent a whole new world, with its own rules, and a logic which follows those rules. For instance, you can have magic, but there must be a price for using magic and logical consequences of the magic.

As for the mechanics, I suggest you think about your main characters. Get a sheet and write down their name, age, address, physical appearance, where they went to school, what their family is like, what they like to read, favourite music, what sports they follow, how they spend their weekends, what they are afraid of, how they speak. You should know your characters inside and out.

Then you can write scenes that are vivid in your mind, even if you are not sure how they get to that point. Write enough scenes and you may find they just slot into place. Sometimes you have to go back and be ruthless about cutting out the ones that don't work.