How should I teach TOEIC?

To make a quick-fix for students' results, try to focus more on technique, i.e. if guessing on multiple choice questions, stick with the same answer, not random. Statistical results show that 'C' is more often the correct answer.

Concentration tips during listening sections, forget that last answer, focus on the next.

Patterns in changing answers, i.e. does the individual usually change from right to wrong or wrong to right.

I had great results using this approach with my students' TOEFL scores.

There are a lot of good books with long sections on technique.

It really depends a lot on what is usual in your teaching context and what students need and expect. However, it would seem to me that you're emphasising grammar too much at the expense of vocabulary & skills. Is your students' output fluent and ambitious enough to warrant exclusive emphasis in accuracy? If not, you may want to broaden your objectives.