I’ve been writing Chinese, Japanese, and Korean characters on regular lined paper. I chose to use wide-ruled paper, which is roughly 0.9 cm between the lines. I think it’s working for Japanese and Korean for now. However, I am only writing hiragana and katakana, and very simple hangul. It’s definitely on the small side for writing Chinese. I think I’ve found practice paper that works.
The paper used by Japanese schoolchildren for writing is called 原稿用紙 (げん こう よう し; gen koo yoo shi). These are 1 cm by 1 cm blocks to write characters. Fumiko Tachibana’s genkooyooshi site has explanations and a pdf file. 原稿用紙 can also be generated at incompetech.com by setting a square size of 1cm.
I tried different values of square sizes and margins to find squares that would be appropriate for writing Chinese. I made large and small squares with the paper generator at incompetech.com. I think the large square practice paper is good for beginners. I believe the square size is 1.5 cm. The small square practice paper works for me, but I cannot remember what size I used to generate it. The spaces between the squares can be a place to write the hanyu pinyin or zhuyin for the corresponding character. I think the small squares will work well for hangul as well.