Some people just think of knots or zoomorphic patterns as Celtic Art but there are a wealth of other types and variations such as the step patterns. In my view, a complete Celtic artist is one who has mastered all of these forms. It is only when all these forms have been mastered that the artist has true freedom of expression and variation. It is not enough to be able to copy them but you must understand their construction in order to create original work in the future. I have therefore given much time to learning these methods. There are many books that can give you some idea of the construction methods and their contents do conflict with one another. The only true way to learn is to sit down and start drawing.