I have been putting up a roadblock about tackling flourishes for so long. I know part of it is just a difficulty I have with spatial things - getting the direction of how to make those curves flow and fit beautifully has been driving me crazy. I was practicing some lettering and thought now is the time because everything is just looking blah. So here are two resources I used to get me past the hump. I also took a photo of the piece that I lettered so you could see that I actually learned something!
I am a big fan of Suzanne Cunningham and I watched her interview and flourishing lesson on the Happy Ever Crafter YouTube channel. She also provides links to a flourishing handout that is very helpful and nice to have.
I found another article called How to get started with Calligraphy Flourishing on the Lettering Daily website. There are a lot of examples explaining the how to use the oval in flourishing and how to apply it. This information also echoed the video from Suzanne.
I hope this helps! Happy flourishing!