Hi! I do work with the Morrigan 
Along with the Pagan Portals series by Morgan Daimler & the links provided by @MeganB, Stephanie Woodfield is a Priestess of the Morrigan & has a couple of books that are worth reading about her too…
- Priestess of the Morrigan: Prayers, Rituals, Devotionals to the Great Queen
- Celtic Lore & Spellcraft of the Dark Goddess: Invoking the Morrigan
Courtney Weber also has a book on the Morrigan with the Foreword by Lora O’Brien:
@SilverBear has a couple of great meditations for working with the Morrigan:
Another good meditation for the Morrigan is:
I work with her & have for almost 2 years. The number 3, crows/ravens 
, horses 
, serpents 
, dragons 
, the New/Dark Moon 
, Samhain, Storm 
Water, Dragons Blood, Sword, the colors Black & Red (such as when lighting candles for Her) & any red juices or wine, red meat, apples or pomegranate, acorns, & those are just off the top of my head right now 
However, the link to The Morrigan: Celtic Goddess I wrote & the sources that I used & links within it also. 
I’m still learning about Her & continue to look into her mythology & history as much as my time allows. I have an incense that I have made specifically for Her & since then my altar & items for Her have changed. Now I work with both Brigid & the Morrigan as my deities. No others have piqued my interest or I guess called to me in a way that I would start working with them.