Attempting to apply what are claimed to be "best practices" to a basic but working Mongoose API fails. Why?

I have a working Mongoose API running, but I have come across a blogpost that suggests that the way it is structured will cause future problems. Specifically, the points said blogpost makes are:

1. Schema should always be declared in their own .js files, one schema per file; and
2. Models should be declared only once in app.js, and made accessible to routes files via dependency injection (ie: one should not use "require" such as var mongoose = require( 'mongoose' );).

I haven't included any code in this question, because I am basically running the example code given in this API tutorial: https://scotch.io/tutorials/build-a-restful-api-using-node-and-express-4

And then attempting to modify it to the requirements outlined by this "best practices" blogpost: http://blog.mongodb.org/post/52299826008/the-mean-stack-mistakes-youre-probably-making