Bring your tongue awareness into your whole body awareness in relationship with each other and the surroundings. In that way you are also aware of your whole body and what happens outside of you. Learn also to allow your focus to shift within this awareness, so you can focus on your tongue (when you need to) without "forgetting" the rest of your body or where you are. Instead of forgetting, you are expanding your awareness so it doesn't feel straining (concentrating on something, be it the tongue or something else, is tiring). 

Expanding your body awareness can take a lot of time and there is no limit. There are people who even claim be able to feel the lymph flow among other things (for ex. Body-Mind centering developed by Bonnie Bainbridge). Of course that's not necessary for mewing, but being embodied can bring a lot of benefits, so don't try to forget your tongue or body awareness. 

But even Mike Mew says one should approach mewing from a whole body perspective. So mewing isn't about thinking only about the tongue. It focuses on the tongue/face, while saying you should work on your body alignment as well. They shouldn't contradict each other. In fact they are crucial for each other.

EDIT:

That was assuming you want to forget, because you are tired of thinking about your tongue the whole time (in case you do). 

But, from my own experience, mewing is some of those things that seem impossible to forget. Even now when I see people's faces, I automatically wonder how good their tongue position is. I can't help it. So I would just try to live with the new info and integrate it to my life in a way I can still think about other things. What I wrote before helps to ease that.

Why?

Well said man, that helps a lot.

Posted by: EddieMoney

Why?

Because of the obsessive thinking of tongue and its posture. I'm stressing myself to press the tongue against my maxilla and Ayla31 helped me out.