Avoid interruptions as much as possible.
Interruptions disrupt your workflow. If you're in the middle of a task and stop to do something else, it can be hard to get back into work mode.
When you're working on a task, try to complete it before getting up to do something else. Other things can wait while you strive to complete something.
Keep in mind, sometimes disruptions are inevitable. If you receive an urgent phone call during a task, for example, you should definitely take the call. Do your best to avoid interruptions, but do not beat yourself up over the occasional distraction during your work.