We always start with tying a horse to a safe place and let them stand there until they get over it. Some will paw, stomp, whinny and fret for hours. BUT -- they all get over it, stand still and relax -- eventually.
Some take a couple of hours, some take two or three days. Tie them out in the morning, offer them a drink at noon (most won't drink and it does not hurt them a bit), put them up in the evening and do it all over again the next day. The good news is that they all get over it.
Once they figure out that there is life and a return to their herd, they get over it. We have found that this is so important to their training, that we do not even bother to try to do anything else as long as the horse is still reactive and acting silly. They learn little except how to fight you and be worried about their herd.
We raise and keep all of our horses in pastures with other horses. So, they all have some degree of separation anxiety when they go into training. We just let them stand tied until they settle down and then they learn other lessons very quickly with little resistance.
We are convinced that if every training session with a frantic horse that is throwing a fit, the horse is only learning to fight training and people. As 'creatures of habit', the habit you want to instill is one of quiet learning and working sessions without resistance or aggression on the part of the horse or the human.
I have seen hundreds of horses that get 'on the fight' every time they are worked with. I think this is the last thing everyone should want to become a habit.