Minimize framework / library lock-in and use well-defined APIs and interfaces to make things as modular as possible. Document your APIs, for JSON APIs, Swagger is a good solution just like WSDLs are great for SOAP APIs. Stick to standards as far as possible, there's a reason those standards were created. Don't jump on the latest greatest frameworks, unless you want to be the one figuring out their problems for them and be the one that needs to maintain that code long after yet another framework has vanished into obscurity. Have coding guidelines that drive the direction the project is taking and also to keep your code-base consistent.