One. Review
Before you leave work, or from your desk at home as you wrap things up for the day (or night!), Take five minutes to review your time at work.
First write down what you accomplished in a quick, bulleted list. Next write what you didn't accomplish that you had hoped to, and what stopped you.
Do not beat yourself up for any failures or things uncompleted. Instead simply notice, if you can, what caused you to get off track. Do notice how much you did accomplish.
This type of review is a way to help your brain focus on the positive (I did accomplish something today) and will help you to become more aware of the things that tend to derail you or distract you from productive work.