At bookstores, I have always been surprised at seeing tons of reference books of keigo (honorific expression) for Japanese natives. However, looking back at my teenage years, I've never spoken in keigo. After I graduated from school and started working, I learned that I should speak with my boss and clients in keigo. Sometimes, even people who are older than me spoke to me in keigo. Hence, I started to learn keigo. 

I think it's not so difficult to master keigo if you know what is keigo like and how to study it. 

To whom do we use keigo? It is not necessarily just towards our elders and betters, as commonly known, but also for certain strangers. For example, even the Japanese emperor talks to me in keigo, because we are not close at all. To pass JLPT or to communicate in Japanese, you don't need to speak or write in keigo but you need to understand and memorise some keigo. 

How to study keigo? To master keigo is to learn the expressions by heart in context. Please note that you need not only understand keigo but also grasp keigo vocabulary by heart.

I can recommend this book, if you really want to master keigo. After you master this reference book, you can use keigo better than Japanese teenagers!