A few things that paid off for me:
Plan your route so that you travel west in the morning and east at night. This means you're rarely looking into the sun low on the horizon.
Know your body's natural rhythm. Are you most alert in the mornings or are you a night owl? I tend to get sleepy at dawn, so I rode those hours early in my trip when I was most alert and was in relatively familiar territory. Planning a gas/pit stop around then also helped.
Remember darkness will slow you down. I'm always watching for the critters itching for a piece of me and consequently I slow down. Make the most of your daylight hours.
Remember, there really is time to rest. Calculate how much rest time you have when you average certain speeds and comfort yourself with this on the road. Rest when you need it.
It may sound simple, but plan a route according to the speed limits. You can't average 50mph on 35 mph roads.
Throw something quirky into the trip like delivering a large birdfeeder to recent home buying inmates. It gives you something to look forward to and breaks things up. It helps if they meet you with homemade squirrel stew and a 5hour energy drink.
Find something that motivates you.
Keep in mind, it doesn't matter if you're lost as long as you keep moving.
If possible, have a friend meet you at the finish line. A friendly familiar face to witness your mileage and maybe pop the champagne will feel like the end of a perfect day!
Happy riding and best of luck!