Hello,

If you're already done with basics of grammar for which the best book is Wren and Martin, then for practice purpose you can refer SP Bakshi Objective General English or Plint to Paramount for practice purpose, other than this read newspaper on a daily basis especially the editorial part this will cover your comprehension part along with improving your vocabulary, you can also refer word power made easy which is pretty good for building vocabulary, and go through practice sets freely available at the competitive exam sites.