Many web development projects are done outside conventional version control environments. The overhead of version control simply can’t be justified for a small application or the customization of a site. However, it the development is performed by a team, particularly a distributed team, common etiquette should be observed.

• Don’t change other people’s code. Either request they change it to your specifications, or ask if it is okay for you to make the change. If you receive such a request, reply promptly and act promptly, otherwise, you should assume the requestor will make the change.
• Keep your own backup. This is a good practice anyway. This includes the database.
• Use a site architecture that makes it easy to separate design and logic, and communicate it to the team. For example - all CSS/HTML/templates are the domain of the design team, all PHP/applications/installations are engineering.
• Identify an authority to resolve any conflicts, and clearly document any likely exceptions to the file architecture above.