The visual rhythm of uniform braids comes from a physical rhythm. So, normally I do one stage of the process at a time. That is: braid the mane down, pull it all up, finesse the bottomline then tie- lock ’em down. Doing one stage at a time lets you get a good rhythm and feel. Plus, it is easier to get the bottomline perfectly straight, which is the most important part of the braid job.
If you have a horses that sits on his tail in the trailer, try clipping him high on the halter. And old timer, that has shipped horses for generations, says that can make the difference. The idea is that when able to move their head more, they stress less.