It good to see your interest in this area. Best wishes ahead!
Regarding your query, there are two worth-mentioning things in this regard. Read Dawn Newspaper especially Editorials and Columns on daily basis or at least thrice a week esp. on Sunday.
Secondly, buy Jahangir's World Times magazine every month. It is usually available after 10th of Every Month at major book points and shops. Even if you don't read Dawn on daily basis, JwolrdTimes Magazine will cater all your needs and will prove a lot in present and coming years. But consult it regularly every month.
At the same time, you can consult English Grammar book for improving your skills in English Grammar and Composition.

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"But screw your courage to the sticking place,
And we'll not fail." _Shakespeare, 'Macbeth')