What Methods Are Used by Mandarin Learners Who Speak Japanese?
Unfortunately, the only good way to practice reading out loud. I would recommend using google translate for each word you don't know how to pronounce and use their pronunciation translator. (Their's is actually pretty accurate).

Luckily though, believe it or not the Chinese pronunciation is a higher learning curve but after that it's VERY simple. There's actually only a set number of sounds for example.

It's good that you know some Japanese so I'm assuming you know some Kanji but also take caution that a lot of Japanese words are not used the same way Chinese words are.

I don't have a computer that can type chinese right now so bare with me or if some one could edit this, I would appreciate it.

For example: The word 'watashi' in japanese is 'I' but the chinese translation of that Kanji is actually 'si'. Which actually means 'personal' or 'private' rather than 'I'.

**Editor's note: 私 is the kanji for watashi