How to keep one's mind open, that is a good question that most everyone has a different answer to. I go by advice I have learned from several sources.
First, allow any thoughts that come up to pass through. Take a quick mental note if it seems important, but don't become attached to the thought. Possibilities for not becoming attached to the thought include thanking it for coming up, asking it to come back when the session is over, or when a thought is stubborn, asking yourself 'who is thinking this thought?' - but do not answer that question!
Second, I have sometimes tried to visualize being somewhere where the sounds of the session would be natural. Second level I would picture myself sitting by a river I used to live near and all the distraction sounds that are part of the recording, birds, wind, bells, were familiar parts of that picture.
Finally, I don't every try to fight the thoughts that come up. If that means I lose a session to mental chatter, then that is what happens. I have occasionally found the times when thoughts overwhelmed the session, the thoughts were actually solutions to long standing problems and it was a positive thing that they occurred.
I hope this helps.
Dreamer