You need to be strict but stay fair, be very rigorous and don't let anything pass. By that i mean that you don't let it go while the exercise neither after it (during grooming, while going back to the paddock...) otherwise it won't be useful.
You can use the "stick to me" technique which is when your horse does the same as you do (you walk slow, they do too, you go faster, they have to go faster too). If your horse doesn't respond and and overtake you, make him go backwards.
You can also make him move his haunches (dominant horses make the other horses move, by that you make your horse understand that you are the leader.)
Finally, you can also use the "join-up" technique but it has to be done by a professional and is only used for dangerous and wild horses.
I hope i could help you, good luck. :)
One of the foundation of good ground manners is desenziting!
If you gaining your horses respect, historia manners won't be bad.
If you have some doubts, contact me!
Hope your question was answered!