If websites distract you there are browser add ons that let you block them for however long you want it. Chrome has StayFocussed and I guess there are others but that's the one I use.
I also find instrumental music helpful. Doesn't matter if something classical, a soundtrack or whatever as long as nobody is singing.

Otherwise: what anon above said. Perhaps slowly 'up' your goals? As in 'another paragraph' before I do X. 'Two more'...