Lots of practice and make the braid as tight and as close to the crest as possible
Make sure that the chunks of hair you choose are rectangular. What I mean is that if the mane looks like this \|\|\|\|\|\|\|\|\|\|\| you will take |\| so it is straight. Not \|\ or \|
It will make sure the spacing and size is even. Also measure the chunk of hairs to the width of something, bigger for bigger and wider spaces braids
Don't use conditioner or showsheen on the mane right before a show if you are going to braid, and a little hairspray never hurt! Otherwise, practice practice practice.
Other than just practicing and repeating the process over and over, you should try to add very small, and evenly spaced pieces of mane, braiding as tightly as possible.