Web 3.0 focuses on semantics, data standards, and understanding through technologies like RDF, OWL, and SPARQL. These standards allow sites and data about the same things to be easily combined and searched. APIs are also important, allowing developers to build applications that access and combine data from different systems and sources, powering mashups, mobile apps, and more. When developing an API, one should focus on RESTful design principles, use meaningful URIs and formats like JSON, and support the developer community through documentation, tutorials, and libraries.