http://www.youtube.com/watch?v=7wttsxM3M78&feature=em-upload_owner
Well, I have already explained the basics of resting the attention on an object & gently bring it back. However, there are generally about 40 concentration objects which yogis focus on, that can take you through the jhana factors.
http://what-buddha-said.net/drops/IV/The_40_Meditations.htm
The 1st 10 on the list, the Kasinas, lead to the development of specific mind powers, & can be read about in:
The Visuddhimagga and Vimuttimagga
http://www.youtube.com/playlist?list=PL321B92FC1DA91E6E
Understanding Concentration