How to write linux drivers?

Hi all, I am linux kernel newbie, I am trying to understand linux kernel since very long. Can anyone tell me how to understand drivers, How can i start working on writing drivers? I just wanted to know that, How can i write the smallest driver and test it? Also suggest me where to find the specification of the target hardware, for which driver is to be written? Ex. floppy drive, bluetooth etc. I want some basic tutorial links also. Thanks Lalit Pratap