Hey there Corinna!
Personally my biggest pet peeve with photos on here is when they're too dark and you can't see what's going on in the photo. I know not everyone has a photo editing program but if this were my photo I'd edit it (in Photoshop) so that its bright enough to where the horse and rider are not colliding with your background but dark enough that nothing seems unnaturally bright. You want to create contrast so the focus of your photo really pops. Then I usually take the burn or dodge tool and nit-pick the details (ie. making the eyes brighter, going over highlights, etc, etc.). Honestly other than that though this picture is done well in my opinion, not that I'm as good of an editor as some of the people on this site but this looks really good to me, nice job