How to Put a Bridle on a Horse

Before putting a bridle on a horse, start with your horse haltered and safely tied. You may have the horse in cross-ties or tied with a lead rope with a panic snap or quick-release knot. Some people like to leave their horses untied, but that can be a problem in public stables where random people may distract or potentially spook the horse. It's best to avoid your horse getting loose among other horses and people when in the stable; this could lead to accidents. Make sure you use a safety knot if you are not using crossties.

You'll also want to brush away any dirt or grit on the horse's face. Before riding, always groom the horse. 
Secure Your Horse
Undo the halter, slide the halter's noseband down over the horse’s nose, and slip the crown back up over the horse’s ears. This action will secure your horse briefly while you put the bridle on. Stand beside the horse's neck, facing forward with the bridle in your left hand. Slip the
 
reins up over the neck. Both the reins and halter are now around the horse's neck, should it try to get away.
Slide the Bit in the Horse's Mouth
Hold the bridle up over the horse's nose with your right hand. Using your left-hand fingers, move the bit against his lips and insert your thumb into the space between the front and back teeth—the bars of the mouth. If the horse resists taking the bit, wiggling your thumb may encourage the horse to open its mouth wider. Slide the bit in and lift the bridle higher with your left hand so the horse can’t spit the bit back out. Be careful around the horse’s teeth; you don't want the bit knocking into them carelessly.
Eventually, you'll be able to do this in one smooth motion.
Pull the Crown Over the Left Ear
Grasp the crown of the bridle with your left hand, and with your right hand, gently bend the horse's right ear forward to slip it under the crown.