I suppose what doesn't really help is thinking generally that I'm not the smartest person in the room, but of course I cannot know until I've checked out everyone in the room and concluded that no one has anything to teach me, which in itself has a faint smell of arrogance. I guess the answer is to start with the presumption that everyone brings some sort of life experience or learning and perhaps there's always something to be learned, even if it's how not to be. The danger of believing you're the smartest person in the room is that you end up writing everyone else off.
Be that as it may, I love the idea of seeking out people with more experience, more knowledge, more insights and particularly more grey matter which is thoughtfully and productively used. The moment you think there's no more learning to be had is the moment your life goes into stagnation mode.
By analogy, John Demartini says if you want to be a millionaire, hang out with other millionaires. If you want to be a billionaire, same principle. If you are happy to be a hundred-aire, hang out with other hundred-aires. Although billionaires may not necessarily be the smartest people in the room, chances are they know something at least about how to make lots of money. There is something empowering about understanding how other people do their lives and it gives us an opportunity to learn how to achieve great things, or how to be mediocre, or creepy, or inspiring or whatever is on offer, depending on our discernment.
I guess you also need to define what "smart" means for you. Is it the people who have made the most money, the ones with the highest IQ (or perhaps the highest EQ), the ones with lots of letters after their names, those who seem to have their relationships altogether, the healthiest ones, the people who are pursuing a committed spiritual path or simply those who who make you laugh? Or all of the above?
For me, the smartest people in the room are those who both inspire me, but still manage to remain humble in their brilliance. It's as simple as that, but if I'm not hanging out with those people, I guess that makes me the dumbest person in the room anyway.