You can go through the stories and poems thoroughly. Always start answering a question mentioning the poet/ author like uparyukt panktiya premchand dwara rachit _ is kahani se li gyi hai. Then try to introduce the poet and then come to your answer. If you remember the story and poems well and those most important quotes and write answers using perfect grammar you are gonna score high in your literature section. Now coming to grammar part, if you are not that good with writing essays please go through at least five sample essays of each type including all solved essays from previous years. Then try to write your own essays in a manner that you learned reading those. Same you will do in letter writing and please confirm the format of letter a ton times. Letter formats can change every alternate months. Just strictly adhere to the formats given in cisce website. Practice a lot of grammer exercises if you want to get a perfect 100. And never ever forget to solve pyqs. Hope it helps. Best of luck!