Jonas Helfer from Apollo did a great write up about his learning while implementing a couple of GraphQL servers. He talks about how to structure your code and which abstractions are helpful when writing GraphQL backends.
Even though this video is already a bit older it's still a great tutorial to get started developing your own GraphQL server. Lee Benson walks you through all the steps to build up a simple database-backed GraphQL backend.
Speaking of writing your own GraphQL server. This great project helps you to use Sequelize implementing the data resolvers of your backend. The most recent release even supports Relay pagination for MySQL databases.