Three important things that help me stay in tune with my work:
1) To start the day off with a task list. It's usually a long one so it kind of keeps me on my toes and focused.
2) Work in Pomodoro - Pomodoro is tomato and it takes about 25 mins to boil one to perfection. So the idea is to work in batches of 25 mins with 5 mins break and a long break after 4 Pomodoro. I sometimes extend the 25 mins if I am into something deep and it would be difficult to get back to it later. There are many desktop and laptop Pomodoro timers so you don't have to worry about tracking time. After a while it becomes a habit.
3) If I think of anything that I need to look into while I am working, I either note it down instantly or if it is something online then I open a browser window and search for it, then I can get back to it later. Writing it down or searching for it helps my mind to ease that I won't forget it.