Hey, to get started with GraphQL on a Node.js backend, you'll first need to install the required packages. Usually, you'd use 'express' alongside 'express-graphql' and 'graphql'. Use this command: npm install express express-graphql graphql. After setting up your basic server with Express, you'll configure GraphQL middleware to define your schema and resolvers. Here's a simple boilerplate:

const express = require('express');
const { graphqlHTTP } = require('express-graphql');
const { buildSchema } = require('graphql');

const schema = buildSchema(`
  type Query {
    message: String
  }
`);

const root = {
  message: () => 'Hello World!'
};

const app = express();
app.use('/graphql', graphqlHTTP({
  schema: schema,
  rootValue: root,
  graphiql: true,
}));
app.listen(4000, () => console.log('Now browse to localhost:4000/graphql'));

This sets up a simple server where you can play around with GraphQL queries through an in-browser tool called GraphiQL.

Regarding efficiency, GraphQL can reduce the number of API calls compared to JSON-RPC as it allows fetching of nested data structures in a single query. However, you'll need to design your schemas and queries to match your specific requirements efficiently. GraphQL is powerful in allowing clients to request only the data they need, which might help in reducing over-fetching compared to traditional API calls.