Ask HN: How to keep focus during work day?

I think nowadays especially if you are working on computer, it's really hard to keep focus on the work. It's just too darn easy and tempting to check email, talk to friends, watch cat videos and read news during your work day. I have done this, I know most of you have done this, but the question is how to prevent this? And how to keep focus on the work? In the end we want to keep our jobs and be better employees.

I have few tricks for this, but before revealing my tricks, I would be more than happy to hear some of yours! and what do you think about this problem?