How's my crystal oscillator layout?

It's a good idea to return the ground for the feedback capacitors directly to the nearest ground pin on the MCU, to reduce emissions.

A guard ring is simply a track connected to ground. It shouldn't have any other connections made to it, as it shouldn't carry any current.

I realize you are using a through hole crystal, but the idea is the same.

In a professionally fabricated board I would have smaller vias allowing me to place more along my shield as well as some under my pic.

As a note, only 1 of the pins on the PIC is ground, but I went ahead and connected an IO pin to ground.

And as another note, it is not shown here, but I a full ground plane that my vias are connecting to.

Guard rings are a term used to describe low-impedance traces that surround or "guard" a high-impedance or sensitive signal. Usually the guard ring is a ground connection, but it can be any low-impedance signal.

A quick google search for "guard ring" with a few other terms (layout, crystal, oscillator) brought up several useful links such as this, this and this, among others.