The previous posts have already mentioned a lot of good practices that can be done to help out not only your tax preparer but yourself.
1) Clear records financial statements like income and expenses categorized, Balance Sheets, etc.
2) Tax Documents and other crucial documents such as closing disclosures, sale of property etc. being maintained and presented accurately for the respective properties. Do not submit unnecessary documents such as minor, consistent receipts. Tax preparers primarily will not need the proof behind the expenses to report if they are just doing the taxes. That is more so utilized in the events where you need to validate the transactions such as an audit.
3) Being involved and understanding what is going on between the properties to be able to answer any questions or concerns that may rise.
As mentioned by others as well, this ultimately depends on the CPA you are working with. Everyone has their own style and preferences to how they operate and may prefer a more hands on approach while others may like to may the process as streamlined as possible.
You can always ask what the CPA would prefer to have a clear idea.