Summarize:

Your horse should already be familiar with riding tack and a saddle pad before you put on the saddle, or else it could get stressed. Have someone your horse already knows gently hold it in place. Your horse will look to your helper for reassurance, so having someone calm nearby will help ease its mood. Don't tie your horse while saddling, which can be dangerous if it gets spooked. Your helper should hold it in place. Since you traditionally mount your horse on its left side, approach it from that side. Rub it with the saddle pad before placing it on its back, remembering to give praise. Heft the saddle quickly and smoothly onto the pad, and let it sit there for 1-2 minutes. If your horse looks comfortable, cinch the girth (saddle strap) just snug enough to keep it in place. Give positive reinforcement when it accepts the girth. Allow your horse to walk and jog around on its own to get used to the saddle. Stay out of the way. It may take several days in a row for your horse to get comfortable wearing the saddle. Make sure your horse has accepted the saddle and is comfortable wearing it before you try mounting. You'll know your horse is comfortable when it doesn't try to remove the saddle with its mouth, flinch when being saddled, or seem skittish when wearing it.
Ask someone to help you introduce the saddle. Place the saddle on your horse's back. Tighten the girth in intervals.