There are loads and loads (and loads!) of horsey blogs on facebook. They all have different styles and USPs, so you have to think about what yours can offer.
There are people on there who are very successful in different disciplines, who focus their blogs on training tips and competition updates. There are also people who blog about their low level competitive activities, either from the perspective of having an unusual mount, confidence issues, or a comic take on what they're trying.
There are people who blog about alternative horsemanship - clicker training, +R, barefoot, bitless, track systems and that sort of thing. There are some - although most of the ones I've seen are very respected professionals - who blog about traditional horsemanship, or common sense hybrids. And some people just blog about what they do, day to day, with their pony.
I've interacted with blogs in all those categories, but my ultimate preference is for those which are well written, humorous and have good photos.