My saddlebred mare also use to have a problem with this. Part of it is training, obviously, but I think another part is that she is so naturally high-set that when shes "paying attention" she perks her head up, and gets out of my reach. Haha! My solution was to just spend about 20-30 minute sessions of just putting the halter/bridle on and off. I would throw the lead rope over her neck first, to "catch" her, and then just pratice, practice, practice. When I bridle her, I make sure to secure the hatler around her neck, so she cant walk off, and I can pull her back to me if needed.
She was also cautious with people around her ears for a long time, once that improved, so did her haltering/bridling. So check that out too. Sometimes it's just the fear of someone/something being around their ears, and not the actual tack itself.