If you use a progressive scheme of magic for a character to go from apprentice to magician, design that scheme before you begin writing. List each stage of development on the profile sheet or index card, and describe the powers, spells, requirements, etc. Try drawing a magic tree, similar to a family tree. Ask yourself questions, lots of them. How magic is gained may have a bearing on how your character views it.
Consistency is essential to believability.
As in all stories, organize your magic tale. It s a quest of having one word flow into the next, one scene, one chapter flowing, flowing until the reader has finished. Especially when the result is a well-written romantic fantasy, a story that allows readers to as if by magic suspend disbelief for the duration of your book.