In writing such a letter, you should do two things. First, you should explain why this inflation is a problem in your opinion. Next, you should say what you think should be done about it.
For the first, I would say that inflation is making it hard for India's economy to grow and to keep up with China's growth. It makes it harder for investors to feel confident creating businesses in India. Of course, it can also hurt regular Indians on a daily basis if their incomes do not rise with the prices.
For the second, there are many possible answers. The Bloomberg.com link below argues that India needs more infrastructure (both roads and electricity) in order to have economic growth and to lower inflation. Depending on your feelings, you might also suggest that the government's (rejected) plan to allow foreign ownership of retail would have been helpful.