I am assuming you are using Package Control for managing your plugins.
What to Sync
Both a list of your packages as well as all of your settings files are all contained within your Packages/User/
folder and that is what you want to keep synced. Assuming that folder is synced, then all you have to do is make sure Package Control is installed and it will automatically install the correct packages based on the packages list you synced.
How to Sync
See this page on the Package Control website for instructions on syncing your settings.
The techniques listed there essentially are either using Git directly in your Packages/User/
folder or are using Dropbox (although the same concept would apply to any cloud service) in combination with symbolic links (since your Dropbox directory and your Sublime Text install are probably not in the same place on your hard drive).