The most effective way to prevent both std and pregnancy is:

Abstinence

Explanation:

he most effective method of preventing STDs and pregnancy. In any sexual education courses, abstinence is the most suggested form of preventing these things from happening. When a person consciously chooses to make this decision it will always lead for the better good

Hope this helps (:

because health skills are tools and strategies and also practical skills are also something you need to learn (like tools and strategies) and put it in reality.