Who taught you to read? For most people it is a pretty easy question to answer. It could have been a parent, sibling, tutor, teacher or any number of people. It is a fundamental skill that serves you your entire life.
Now where did you learn how to write? This is a bit of a trickier one to answer because we are taught how to write bit by bit, piece by piece over a long period of time. During that time we hopefully develop our own style, but it is all too easy to pick up some bad habits from our teachers. Also since it does happen over such a large period of time sometimes we find ourselves not knowing a certain writing technique when we need it, or forgetting it when we want to use it because we learned it far too long ago and completely out of context.
Just as every other skill in life it is important to take time to learn more about writing if you would like to be serious at it. At the very least it can lead to inspiration or give you the proper motivation necessary to finish writing your book.
This does not mean you have to go back to school, although that is a terrific option. Fortunately for all of us there are dozens of great writing books in our local libraries and book shops. If you are a procrastinator, like I can be, I recommend the book No Plot? No Problem!: A Low-Stress, High-Velocity Guide to Writing a Novel in 30 Days. However if you would simply like some basic (and not so basic) advice on technique the book Writing Fiction For Dummies is a priceless treasure.
However you re-learn how to write you are sure to be doing yourself and your readers a great favor by giving your story that extra push towards greatness.