First I'm gonna explain the diffrent prayer's and thier uses.
Thick skin: It increases your defense slightly aka 5% you must be level 1
Burst of strength increases your strength by 5% and you must be level 4
Clarity of thought increases your attack by 5% and you must be level 7
Rock skin increases your defense by 10% and you must be level 10
Superhuman strength increases your strength by 10% and you must be level 13
Improved reflexes increases your attack by 10% and you need to be level 16
Rapid restore refills all skills except prayer and hitpoints 50% faster and you must be level 19
Rapid heal restores hitpoints 50% faster and you must be level 22
Protect items keeps one extra item if you die and you must be level 25
Steel skin increases your defense by 15% and your level needs to be 28
Ultimate strength increases your strength by 15% and you must be level 31
Incredible reflexes increases your attack by 15% and you need to be level 34