The secret (or so I understand) is:
- If there's something you need the audience to know, but it isn't immediately important, mention it in passing at least three times in different ways. ("My mom was from X country." "Oh, I've been dying my hair so it's less obvious I'm half-X." "I speak a little bit of Y language, but my X accent is pretty strong." Spread it out though)
- If you have a big reveal, "beg the question" to ensure your audience is thinking about it. (mysterious mentor accidentally reveals an ornate sword at their hip; young naive protag asks where they got it, mentor evades before saying something about guarding caravans; shortly afterward the protag realizes that that couldn't be the truth, but the moment has passed. Audience: "But wait, how did they get that sword??")
- If you have a story detail you want your audience to care about, make a sympathetic and/or PoV character show an interest in it. ("I've always wanted to visit Setpiece Canyon! They say you can still hear the ghosts of the people who died in That One War, but I mostly want to see the sunset reflecting off the glassy tomb of King Wontstaydead. Too bad this kitten rescue I run doesn't leave me with much vacation time...")
- If there's something that will help your audience figure out a reveal early, mention it in the middle of a longish sentence because primacy/recency bias; at best, it gets noticed unconsciously, and at worst your audience can't pretend they weren't warned about it. ("There was a beautiful, ornate chandelier above the banquet hall; a huge, murder-weapon-y butcher's knife jutted out of a perfectly-cooked turkey at the centre of the table, and the surrounding plates begged to be stacked high.")
- If you have a reveal that you're afraid is very guessable, come up with an even more guessable reveal and put it in the way. ("I've been looking into these secret government programs surrounding the rise of superheroes, and I can't shake this feeling that-" "Hold that thought! The Tedtonator is just outside, fighting a crime! Man, where'd our perfectly normal buddy Theodore go? He'd LOVE this!")
...Though if readers think a central character is a horse (and they are not), then I'd maybe start with dialog and character agency instead...