I don't tie them at all, I just start small in an area with no grazing because grass will make even the best of horses lose focus on the task at hand LOL.
I just put them where I want them, tell them "whoa" and start to walk away. If they move or follow me, I put them back where they were and tell them "whoa" again. Every time they move when I start to leave, I do that. After they've started standing while I walk away, I'll go 10-15 paces and stand with my back to them for a bit. Again, if they start to move, I'll go move them back and try again. Then, when they are standing steady for that, I'll ask them to stand and then I'll walk around the corner of the barn or into the tack room where I can watch them but they can't really see me. I'll stand there for a couple of minutes and then go back out. If they haven't moved, I'll praise the heck out of them. It's up to you whether you want to treat them or not at that point. Some of mine I do and others I don't.
Just keep repeating this process for longer periods of time until they will stand indefinitely with you out of sight.
Of course, no horse will ever ground tie 100% of the time without a person present because they are about like kids with the short attention spans and easy distraction, but most of the time it works.
4 year old horse with maybe 75 rides, hadn't seen a saddle in weeks. I led him out of the barn, told him "whoa" and he stood like a rock for around 5 minutes while I took care of the dogs around the corner of the barn.