Protect from Missiles offers players 100% resistance to most NPC ranged attacks, and 40% resistance to player-dealt ranged attacks. It depletes prayer at a rate of 1 point per 3 seconds (or 5 game ticks).
Protection prayers only reduce damage. They don't have an effect on accuracy. 
A strategy to use as few prayer points as possible without losing the respective effect. Players may turn on their chosen prayer just before being hit by an enemy, and then turn off the prayer just after being hit. If a player does this extremely accurately, no prayer points will be lost (as the prayer will be on for only a few game ticks).
<ref>tags exist, but no
<references/>tag was found