I live in France and need to apply for a visitors visa to Shanghai to see my sister how do I do it?

You can just apply for a China L family visit visa from the nearby China embassy or consulate-general with your passport, China visa application form, round-trip air ticket, invitation letter from your sisiter and copies of your sister in Shanghai's passport and Chinese residence permit.

Thanks for the info.
I have booked my ticket, so that is okay. My sister isn't actually living there at the moment but is moving there in August to a serviced apartment whilst the house they are renting is renovated, does she need to write a letter inviting me with address etc..
Thanks

yes, her address is needed in the invitation letter.