What I do, is every half an hour or so give myself 5 minutes to do something you enjoy, listen to a song or put on the radio or flick through a magazine. It seems to help me a lot for someone reason and I find it easier to concentrate after taking my mind of work for a few minutes.
Also set yourself short term goals e.g. to finish a chapter or topic in an hour. It will make the work more achievable.
Also allocate hour long breaks for tv programs etc. Then you have something to look forward to when you’re working, it seems to motivate me to get things done so that I can allow myself a small break.
You probably knew all this anyway, but hopefully it helps.