The National Archives guide to Domesday is a good starting point for study. There are also several on-line versions of the book (beware those that try to charge you for an extract). The best is domesdaymap.co.uk. Here you can search by place and person, view facsimile images of the original folio volume, read a digest of each entry and generate your own interactive maps. Below for example is the entry for Geoffrey Alselin, Lord of Laxton in 1086.
There is also an interesting report by English Heritage on mapping Domesday data: Lowerre, A. 2008. Mapping Domesday Book using GIS. Research News: Newsletter of the English Heritage Research Department. Number 8, which may be downloaded from here. And as if that wasn't enough, Darby and Maxwell's classic Domesday Geography of Northern England is available as a free Google E-book from here.
