What do you need to prepare in advance to learn composition from scratch?

Theory is essential. The four blocks of composition, harmony, polyphony, orchestration and musical form, should be understood from the shallow to the deep, but they cannot be framed by theory. On the other hand, we should keep our inner sensitivity, feelings about our own voice and feelings about ourselves, so that we can better express our ideas in music. We should also analyze other people's works more, and then practice more by ourselves, so that we can write well if we write too much.