I've been a remote employee for 10 years now (plus 4 being a freelancer) and I've tried every productivity hack under the sun and the only thing that has worked for me is: do meaningful work.
And be ready to catch that wave of productivity when it hits. Personally I can't work 8 hours straight. I try to make work a part of life, and it's not bad since it's a creative job. Have some structure to fall back on but take advantage of the flexibility when it is useful. Get Excersise in during the day, your mind a body will have more energy. Go to a coffee shop/library and get around other people. Get in your 8 hours in the most comfortable way possible.