The only and the most significant common thing in Chinese and Japanese is the usage of Chinese characters(Kanji).
But they use simplified ones in China; traditional ones in Taiwan; middle way in Japan. The pronunciations of Kanji are highly related, but not the same at all. The vocabs in Kanji, some are shared, some are slightly different, and some are totally different.
Other things, such as grammar, are totally different. Yet we Japanese understand Chinese if written to SOME extent because we share Kanji. But I don't know if it will benefit you or not.
When you get advanced in both languages, you may find that there are some shared cultural things, such as Buddhism, Confucianism, Chinese classic literature, food etc., behind the language. But it would not be a matter until much later, I guess.