There's a reason I play this song every time I write.
There's always a burden I bring into my writing sessions: this book sucks; it will never sell; I should go grocery shopping; my inbox is full of unanswered emails; where the heck is this plot going?
I have to clear out the nagging voices in my head before the real voices, the creative ones, can start speaking to me. I used to prepare for writing by making some tea and trying to meditate while it brewed. That worked well enough. Then Frozen came along, and my pre-writing routine seriously leveled up. Now I belt out Let It Go every time before I write (or, you know, do it in my head if the kids are home).
Find a routine that works for you and use it, consciously, to open those subconscious floodgates and produce your best work.