What are useful tips and tricks for collaborating remotely?
A good Revision Control!! I use Git coupled with github being an efficient way (and free) to share and complete a collaboration, especially for code and latex files. 

Else, google docs is also free,  allows to multiple persons to edit the same file at the same time, and you see who is doing what. You can do most "Microsoft Word" formats and things. You have also have as service free video-conference and chat.

I highly discourage Dropbox to share files edited per more than one person.