Hello Aspirant,

There is only one solution to your question , that is reading . Developing a reading habit on a daily basis is the most important primary step towards achieving good language skills or to imporve vocabulary.Read whatever you can,be it newspaper, books,posters,articles and so on.Even while watching english movies read the subtitles.But reading alone will not be enough , the next step would be to use what you have learnt by speaking and writing . Along with reading habit, develop writing habit too. Some  vocabulary development books are " Word power made easy" by Norman Lewis, "The vocabulary builder workbook" by Chris Lele, "All about words" by Maxwell Nurnberg .You can use many online apps too which are built for improving vocabulary ,these apps will have many quizzes which you can play whenever you are free. But do not simply rely on apps and self help books , make reading a serious habit.

All the best