Dear Friend! I shall recommend that you first try to read Pashto books (especially poetry as the essence of real Pashto lies there), analyse newspapers (especially its articles) like QUDRAT and DAILY WAHDAT, surf sites like:
http://www.bbc.co.uk/pashto/
http://www.voanews.com/pashto/news/
http://pukhto.net/
http://learnpashto.wordpress.com/
etc....
After that, you need to write on different topics from whatever you'have studied and gathered, and make a coherent whole of it. Moreover, you also have to meet Master Pashto students as they will be of substantial help to you in carrying out all this.

Best of luck!