Michael Cauchi did a very neat detailed tutorial, concentrated on character grooms that use guide curves but it’s got a lot of other info as well.
Animator and 3d artist Michael Cauchi shared a lot of cool content with the community in the past. Most recently, he did a very nice tutorial on using XGen in your pipeline.
XGen is a geometry instancer that lets you populate the surface of polygon meshes with an arbitrary number of primitives either randomly or uniformly placed. In simple English, XGen is great for procedural hair, fur and feathers. It could also be used for large-scale environments when you need to cover them with grass or rocks.
Michael’s tutorial mostly centers on character hair. Here’s a little abstract from the post.