The quickest way on how a person can learn composition is by memorizing fragments of music and then, learning to combine and change those fragments in specific ways. The procedure of changing it is what forces you to understand it better. Actually, this is a lot closer to how composers were taught before. Believe it or not, composers similar to Beethoven, Debussy, Ravel, Mozart and Bach were taught in such a way.
Do You have the Will?
In learning composition, you should be ready because this is something that takes time. There are a lot of things that you do not know and that is totally fine. After all, everything starts with background knowledge. Everything that you have learned in music up to this moment will give direction to your learning pace.
Then, you focus on a specific composition skill, one step at a time. This may be something as small as correctly writing notes or as major as symphonies.
Challenges and Goals Unique to Understanding Composition
There are of course challenges in composing and it is extremely important that you know what you are up against. Most of the following will be familiar to you like having too much information to digest, endless possibilities, difficulty in composing without having inspiration, incapable of transcribing what you have heard in your head or meaning, having a different sound than what you have imagined.
These are all normal. You’ll go through this process but you have to overcome it and get used to it.