There are many different approaches one can use in order to teach a second language but not all of the suited for every student, nor for every teacher for that matter; as future teachers it is our ethical duty to familiarize ourselves with each and every one of these approaches, their methodology, history, design and the different activities we as teachers can use with each one of them.
Unfortunately for most students in this day and age go to schools were the only requirement for the teacher to work there is to have very good pronunciation of the language and basic knowledge of grammar even though there have been reforms made to the education law in the country, most schools just have to request permission from the local government to hire an unlicensed teacher due to the shortage of well-prepared teachers.
I must admit that this was my case up until a couple of years ago that I started studying this
career and learned about all the different approaches in language teacher that
exist, which placed me at an advantage because I got the opportunity to use my
students as guinea pigs and was able practice most of them first hand inside my
classroom with various different stages of success and failure.
The most useful approach that I
found for teenagers was the direct approach because since the use of the native
language is not allowed and emphasis is greatly made on the target language at
all times, it forces students to directly associate objects and concepts from
their native language into the corresponding words of the target language
making its primary goal to have students think and speak in the target
language. 
Since use of the native language is
not allowed or at least should be avoided at all times we as teaches have to
rely heavily on the use of different objects, visuals and realia in order to
make learning (input) comprehensible for our students, the classes must revolve
around specific topics and grammar must be taught inductively through the
management of that topic so that the students may draw their own conclusions
about the grammar with the guidance of the teacher. 
