If you find concentrating hard, try these tips:

CLEAR EVERYTHING

Clear your desk.
Turn off email/phone ringer/alerts/texts.
Put on your headphones. Even if you don’t listen to music, you will prevent [most] people from approaching you.
If someone comes over, know what you will say: “Hi Joe, I am heads down working on an urgent deadline right now [this may or may not be true]. Can we have this discussion in 2 minutes or less? Or, how about sending me an email with the request and deadline and I will respond by 3 pm today.”
Set a timer (20-30 mins) to focus without distractions.

DO IT

Do the task.
If you can concentrate longer than the time, keep going as long as it doesn’t take up time you scheduled for another task.
Once you find yourself getting distracted, STOP and refresh.

EVALUATE & ASK

Did you concentrate for the whole time? If not, what distracted you? How can you prevent that next time? Do you need to set smaller amounts of time to concentrate for, or maybe find a quieter less distracting space to work in?
How far did you get? Determine what of the task is left to do. Decide if you can take a short break and continue working or if you need to revise your schedule.

REWARD!

Figure out your reward system: do you take a 10 min break, watch hilarious cat YouTube videos, check your email, go for a walk, call a friend…?
Reward yourself and/or take a break.
Start the cycle over again.