Well, if you already are awake at these times, this is what I do:
Shower first thing so that you start off refreshed. A lot of people get some of their best thinking out in the shower.
Sit down with a coffee and nice breakfast at a workstation free of distraction. I usually clean off a spot on my table the night before.
Have a list of things you want to get done before 8. For example: Read X paper and summarize their points on Y, or Write 1 page of methods for Z study I'm currently working on. Be realistic about what you can get done in that amount of time. It's harder to stick with something if you feel like you're never completing the entire task.
Start in smaller bursts. Maybe 30 minutes of writing, 30 minutes of relaxing, and repeat. Eventually, you can get it to 50 minutes of writing and 10 minutes of relaxing per hour burst (or 2 straight hours if you want).
Last bit of advice here: If you're not a "morning person", don't try to force yourself to be. Find 2 hours in your afternoon, where you could be more alert and productive. Take the tasks that you might normally do in that time frame, and move those to the earlier hours. These could be laundry, paying pills, sorting references in a citation manager. Anything that could be moved to another time, but requires less brain power than actually writing. You can use those free hours for writing, and get more done in that time frame too.