0.) Don't use sth like zip-file based pseudo version control! On no platform!
1.) Define yourself the terms on which you want to collaborate, like regular communication / who is working on what
2.) Use a Source Code Control system like git or SVN, but don't just use it for the sake of using it. Each tool can be applied suboptimally / wrong. Coming back to 1.) --> know the tool features you need to implement your workflow.
3.) Use a managed instance of whatever SCC you are using. Don't get bogged down with maintaining this as well. I do take it as a given, that the SCC instance is backed up regularly.
To state it clearly: SCC is no backup system
