I practice calligraphy with A4 paper, paper and other waste paper, but some points and strokes are always out of place. Is it because I don't know kung fu, or should I use rice paper?

A4 paper is not suitable for practicing calligraphy, but waste newspapers can. You can use fringed paper. But your problem is mainly that kung fu is not in place. Xuan paper is too expensive for beginners. Real rice paper should contain more than 40% sandalwood bark. Now many well-known "rice paper" have no sandalwood at all. Besides, it is too expensive to buy real sandalwood rice paper.