Bitless bridles work best when correctly fitted. This page describes how to ensure the best possible fit, both in terms of comfort for the horse, and effectiveness.
A Dr Cook Fitting
This fitting shows New Forest pony Dolly modelling her Dr Cook Bitless Bridle.
These first two photos show the bridle on her from both sides.

The Bitless Bridle needs to be fitted properly to ensure that the horse is comfortable, and that you can use it effectively. The noseband should be approximately two fingers away from the corner of the horse's mouth (this is a rough guide and changes from horse to horse. Please see the diagram below kindly supplied from Sheila at www.bitlessbridle.co.uk showing the noseband fitted just below the pre-maxillary notches). It should be fitted pretty snugly - you should however be able to get a finger between the horse's jaw and the noseband.

The cheekpieces should be tight enough that they won't flap away from the horse's face when you tighten the reins. The easiest way to get the tautness correct is to slide the flat of your hand between the cheekpiece and the horse's cheek. Your hand should fit snugly.
The headpiece should be snug, but still have enough room to fit a hand under the headpiece and browband - it's amazing how many horses "misbehave" because their bridle is pinching their ears!

The cross-straps should cross in the middle of the underside of the horse's face.
English hackamore

This picture shows a correctly fitted hackamore. The noseband is fitted high enough to not impede the horse's breathing and when the reins are tightened, the cheekpieces don't get too close to the horse's eyes.
Rope Halter tied as a Bosal
This rope halter is well fitted. The noseband is neither too high nor too low, the cheekpieces are well away from the horse's eyes and there isn't a lot of excess rope under the horse's chin to confuse the signals she receives from her rider.