Every year thousands of candidates are disqualified because they fail to clear either of these 2 exams. The process is that first UPSC evaluates the language papers, and if you qualify them, only then your GS, optional and essay papers are evaluated.
All your hard work would go to waste if you fail to qualify the language papers.
For people who are weak in English, buy a good gramma book, a dictionary and last 10 yrs english papers. Start working on this from now onwards.Even people whose english is fine, plz do not forget to buy the last 10 yr questions and go through them to see what kind of questions are asked just so that you are not surprised in the exam.
Same thing would hold for regional language papers. I had opted for Hindi, as it is my mother tongue. But I hadn't written Hindi since 10th, So it was rusty. I practiced writing Hindi and Hindi grammar before exams. Eg Idioms, synonyms etc.
Please remember, do not be overconfident with regard to these papers.
They are of a qualifying nature, but probbaly the most imp.
All the best!!!!