What adds need to die first? Spellcasters? I see a rogue type, and hunter type. Maybe even a warrior type.
After you've been in the fight a couple times you'll grow familiar with the adds a bit more. Typically I focus on the one's with most health because they also tend to be the most dangerous. On the first door I believe it's the guys that form the sand pools. The third door it's the frozen warlords, I believe, that drop the frozen orbs. Feel free to hit Horridon a bit at the very beginning for about twenty seconds before the first door opens and then in between doors when all the adds have been killed. Dinomancers obviously are your main focus when they come down and click the orb it drops at 50% health if you can and nobody else has done it as that's what gets Horridon to crash into the gates.
That fight is progressively becoming my most frustrating one because people are so concerned with being #1 on the damage meters that they only attack Horridon and things can get really messy. Especially because a door will be open and the war god will get spawned and things can go to Hell fairly quickly.
If it says Horridon is going to charge you you're best move would be to run to the side away from other groups of people but it's not super important. A lot of people just don't care and soak the hits because they don't want to move. Regardless, as said, the charge is done randomly to people and just means that he's going to double swipe where he charges the person so if it's you keep running sideways to get out of the swipe.
You know what? I really can't wait for Flex raids as that'll hopefully allow fights you don't beat your head against but also require proper mechanics and awareness. And it's essentially with people you know, or at least have to be more accountable, so they won't play as stupidly.
Why don't you jump into the other wings? I know from your previous posts that you're typically very cautious moving forward with your LFR runs but I think you'd enjoy the possibility of all the gear you could be getting from doing nine other boss fights. And I doubt anyone's going to call you out or get upset about your performance as long as you're not running forward and pulling the boss before people are ready. And just be open and ask someone to whisper you fight details and usually at least one person will give you the absolute basics you need to know, be it either who to attack, attacks to watch out for, or particular movement needed or something. And just be ready to die. It's your first time in there. Most of us died on our first time on certain bosses. I died multiple times on Durumu before I finally recognized what to do correctly. Ji Kun was a mess as well. The more LFR you do the more comfortable you'll get and more confident you'll be going forward.