Here is a combined list of the Sync tips:
“Successful Sync Tips” ~ Family Tree Maker 2012
[Tips collected and edited from Ancestry.com message board http://boards.ancestry.com/topics.software.famtreemaker/9684...
Several people have reported successfully using the TreeSync feature of Family Tree Maker by following some or all of these tips. Most highly recommended tips are flagged with (*).
1. (*) Sync at least every day that you make changes to either the online family tree or to Family Tree Maker (FTM). Sync in low volume even if it means syncing more than once a day. Don’t wait a week or weeks before syncing the Ancestry.com family tree to FTM.
2. (*) Don’t ever cancel a sync once it is started. If you have to close FTM before it finishes — if it hangs or for any other reason — use the Windows Task Manager to close it instead (Ctrl-Alt_Del keys). This takes you back to before the sync started, rather than saving part of the sync or not saving part of the sync.
3. (*) Set the sync option to Manual (not Automatic) to control the sync process yourself.
4. (*) Make your changes in FTM or Ancestry.com, then sync to the other one.
5. (*) Sync data in only one direction at a time. If you modify the online tree, sync to FTM before changing ANYTHING in the FTM tree. If you modify the FTM tree at all, sync back to Ancestry before making ANY changes in the Ancestry tree.
6. If you make almost all tree changes in Ancestry, then sync to FTM. Then, resolve places in FTM and sync those changes back to Ancestry. It doesn’t matter which one you do your primary work on, as long as you have a consistent system.
7. (*) Compact your FTM file regularly [Tools Menu, Compact file]. Some people recommend doing the Compact every time BEFORE they sync their trees.
8. (*) STOP the timer during the sync and look at the Sync Report before going forward. SAVE each sync report to PDF and check it to make sure that there is nothing unusual showing or any people that you did not make changes to. If there are anomalies on the report, close FTM using Windows Task Manager (not Cancel) and re-try the sync. Known sync issue: the media names are not attached to the right people; the name of one media item will be repeated for everyone who had any media changes (since the latest patch FTM version 126.96.36.1993)
9. Create a backup immediately before synchronizing — every time.
10. Save backups with different names and never over-write — ever!
11. Media and photographs are copied after the main sync. Open the Plan View after sync finishes. There is a small bar showing the progress of media upload/download. Don't close FTM until the media finishes syncing.
12. Log out of Ancestry.com or close the browser window while syncing in FTM.
13. Turn off “cloud” or “connected” services such as Dropbox while syncing.
14. Keep track of your counts on Ancestry.com and Family Tree Maker and check them to make sure they are what they should be.
15. Add FTM.exe to your virus and/or firewall program's Exception List or White List. [added 9/27/2013]
Since using these tips, I went from trying to sync weekly, and then only being able to sync once or twice before having to re-download my entire tree — with resulting major frustrations — to successful syncs every single day taking 5 minutes or less. I also back up my tree to an external hard drive every day after I sync.