1) Eliminate distractions
For me this involved conciously blocking some website on my installed browsers. While I put this off for a long time, because I convinced byself I would merely circumvent the block when I wanted to view the site, this really helped. Somehow having the site return as blocked was enough to snap me back to what I needed to do. Keep your PC work environment clear of distracting programs you should not be using, and make them more difficult to access. Surprisingly, its much easier to convince your mind to not do something if you add extra steps required to do it.
2) Make Lists
A list of tasks with an approximate timeline will encourage you to stay on taskIf you don't have something specific you wish to accomplish in a particular time, its easy to get distracted. As David Allen explains in Getting Things Done, it's helpful to break down goals to the next Actionable step, the next action you have to take to complete a task.. Its important to be realistic, but not be too forgiving with time allocated to tasks, or you will doddle.
3) Limit Time
Use the Pomodoro Technique, or something similar to set a time window where you will commit to being completely focused. Any distracting thought that comes to mind should be recorded for later, not acted upon. You lose tremendus productivity by context switching
4) Remove Automated Distractions
Unless the work involves your Email, do not check E-mails between bounded time windows, and don't have your Email client automatically refresh incoming mail. Turn off social networks, or anything else that automatically interrupts and distracts
5) Keep it simple
Don't try to make time management too fancy. If you system has too much overhead, it will reduce productivty and be tedious. Also, stick with your system, and don't try to reinvent it every week. There is a point where looking for new productivity hacks becomes a way to procastinate.