Mindfulness practice is about becoming familiar with your mind.  It doesn’t matter if you struggle to stay focused - observe without judgement what is on your mind.  Accept and familiarise yourself with whats going on in your mind, in the moment. 
Read more  at http://blog.beliefnet.com/mindfulnessmatters/2012/04/obstacles-to-practice-agendas-expectations-and-striving.html#ixzz1sSU1mAyM