I read many posts on 200WAD from people who do not know what to write about. These posts are from writers who are new as well as from members of #Teamstreak. It happens to all of us from time to time. One reason this may happen is you are sitting down to write when you are not ready to write.
There are some people who wait until the final few minutes to write either because that's how they planned the day, or unforeseen circumstances, or perhaps they like the pressure of writing and the risk and danger of breaking their streak.
Martin Weir: "What's the matter, the pressure got too much for ya?"
Chili Palmer: "Pressure..? I'm the one who applied the pressure."
--From Get Shorty
If you sit down with 30 or 20 or 10 minutes before midnight, now you HAVE to write. For some people, this pressure unleashes creativity. For others it creates a block.
There are others who schedule a specific time to write every day. This scheduled time could also create pressure if it's the only time you allow yourself to write. You sit down at the computer and say, "Ok it's time to write now." Some people successfully write every day with this approach. I used to do this but found that it doesn't work for me.
I have learned to write when I'm ready to write. Sometimes I have an idea first thing in the morning. Other times an idea strikes in the middle of the day. Even if I am unable to write a post in that moment, I write the idea down so I don't lose it. This makes it easy to write when I have free time.
One piece of advice for proper "sleep hygiene" is to only do two things in bed: sleep and sex. If you watch TV or read while in bed, this may cause you to associate other activities besides sleep with the bed. If you get into bed and cannot fall asleep, the recommendation is to get out of bed. In other words, when you are sleepy you should go to bed. You shouldn't go to bed and wait to get sleepy.
The same applies with eating. You don't sit at a dinner table and wait to get hungry. You get hungry, prepare a meal, and sit down and eat it.
I apply this same approach to writing. I don't sit down at the computer and force myself to write something. I have ideas and things to say first, then I sit down at the computer to write them. I write when I'm ready to write, and this prevents me from sitting and staring at a blank screen waiting for inspiration to strike.