The whole world of learning English revolves around the four skills, i.e., Listening, Speaking, Reading, Writing. These skills are sort of dependent on one another. If someone wants to excel both at speaking & writing skill then one must make sure that they're giving equal amount of time to all the aforementioned skills. Now it solely depends on you that which part you want to be good at, either Speaking or Writing or both of them. But in order to get through the written part of the exam one must have an excellent writing skills & it doesn't matter if someone isn't good at speaking English (But being good at speaking helps candidate later in an interview ).

To improve writing, read English newspaper calmly & if you encounter anything which you don't understand then consult it at the spot, whether it be a grammatical stuff or vocabulary or idiom/phrasal verb or whatever, and write daily on a paper or have a discussion over here with members. To improve speaking, watch english movies with subtitles plus seasons are also useful, there are live english news channels out there on internet, go for them. Plus the last but not least the damn youtube which is unblocked in Pakistan now, has a whole lot of videos of "Goras" which you can see to improve your speaking skill and speak with the ones you are surrounded with, doesn't matter if they laugh at you. If you are alone then talk to yourself in english. Speaking and writing can only help you make good at whole english stuff.