Since you do self-care and prep and show at a hight level, I would think many readers would be drawn to a detailed chronicle of that. An elaborate synopsis of your day with the showing itself as just a small component would probably appeal to a large readership. Readers love something with which they can identify. I would think there are tons of riders who would really relate to your chronicle of preparation for the shows and then a detailed ‘show day’. I’ve read many start-to-finish horse show day blogs and when done well they are quite interesting.
All of that said, as stated above there is an intangible aspect to what makes a great blog. I read every.single.post of this blog http://dreadfulacres.com/blog/ as she is one heck of a funny, articulate, and interesting writer. She articulates every day, sometimes mundane things in an compelling and humorous way. I wish she would keep going with it. My best friend writes a horse-specific blog that I think is terrific http://riderwriterfarmerwife.blogspot.com.
Style aside, just try to be relatable. You know what you enjoy reading - try to put your finger on why you enjoy it. I would say don’t get bogged down in the details of showing, but more in the ‘applicable to most’ aspects of life. Talk about your fears, frustrations, heart aches, nerves. Everyone can relate to those feelings, from those about to compete for the first time to those veterans of the GP ring.
And thank you for your courage in sharing your experiences through a blog. It’s sometimes a scary thing to put oneself out there and it’s commendable that not only do you want to do that, but you want to do it well.