One of the things that I have found true is that you can not "force yourself" to write.
However, you can do a few things to make life easier:
1. There are always several different writing projects / options available.
That gives you variety and choice. They may not be in the mood for a topic, but may have the motivation to focus on one another.
2. Warm up your brain.
By that I just mean the whole "garbage" as a warm-up phase for your actual writing session.
Many people are held back because they do not know what to write and eventually fall into a river. This usually helps to get to that point of the "river".
3. Showering, walking, exercising, yoga etc.
Especially if you have researched something, this is a great treatment for you and your mind.
Have you ever had a "ah ha!" Moment falling asleep or showering?
Same principle …
They give your subconscious a chance to break down all the information you've consumed and now have the chance
do some of the "heavy lifting" for you.
I hope that helps!