The most straightforward example to make you familiar with how to create a custom SPFx Yeoman generator is to use Yarn instead of NPM as your default package manager. The approach to change the default package manager is simple, and many people already use it as there default package managing solution.
So, instead of adding the ‘–skip-install’ option whenever you start a new project just add this option to a generator.
The first step is, as always, to create a new NPM package.
Whenever you start a new SharePoint project, you might depend on external libraries. These libraries are maybe small helper tools such as jQuery or maybe like to go beyond KnockOut or React. Let’s say you want to use Handlebars, VueJS or perhaps Angular 1.x. 
Everything you perform the same setup steps in the same order. In my case, I start most new projects using Handlebars. Luckily I wrote my documentation to make the configurations pretty smoothly. To be honest, it is proper training but on the other hand a complete waste of time. Why not automate my personal preferences and start a new project from scratch with my settings already applied. This article takes a look at why you might consider writing your own SharePoint generator in future. [Read more]