Since I'm going to indulge in some backstory, I'll lead with my thesis, so you know where we're headed: You're probably bad at perceiving, and your product suffers as a result. Hard to believe you're bad at something you've been doing you're entire life, right?
v1: Seeing Like a Tourist
This summer I hosted some first-time visitors to New York. As I showed them around, I shared the joy of experiencing Manhattan through their eyes. I found myself deviating from routine, taking routes I would never take. I found myself pausing to observe, when ordinarily I would rush toward my destination. And, most interestingly, I found my gaze widening, to just take it all in, even routine things my eye now automatically, unconsciously ignores.
I struggled to name this mode of observation, but "Seeing Wide" seemed close. Where ordinarily I would only look where my eye expected to find novelty (things that change often) or utility (affordances that help me accomplish my task), through their eyes I stepped back to take in the whole gestalt of the scene, and I devoted a lot of attention to observing parts of the scene that I had learned to ignore in the name of efficiency and purpose.
Since then, I've tried to intentionally observe in that way from time to time. It would be sad, I've thought, to only experience that joy when tourists give me an excuse. It's especially enjoyable when leaves are falling, or when I find myself on a rooftop with a great angle. This Thanksgiving, in Los Olivos, California, I spent an hour or two staring across the beautiful landscape trying to meta-observe how my eye was choosing to look at some things and ignore other things, in an attempt to un-train myself from focusing in on parts instead of seeing the whole:

v2: Seeing Wide
It dawned on me that this mode of observation can be professionally useful -- and that product managers don't do it often enough.
Most product managers--by personality and by professional need--have a natural tendency to unconsciously abstract what they see and not actually revel in the glorious detail. Partly it's how we're built; partly it's out of a need to think more strategically, at a higher level. Either way, we don't even perceive a rounded polgyon with lettering and gradients and whatnot -- our minds have wired themselves to unconsciously filter and categorize it as a "submit button" and from then on, we perceive it not as it is, but as we have categorized it.
In the language of Myers-Briggs, most product managers perceive information intuitively (matching it to expected patterns) rather than through direct sensing (seeing the detail first) -- by default, that is; unless they consciously think about perceiving differently.
Perceiving intuitively has its benefits. Someone in a product design team needs to be thinking abstractly and strategically. But it has costs, as well. You (the product manager) may not have the same set of filters, categories, and expectations as your users, and so you need to be sure you're not viewing your product as a product manager, but rather as a user would.
How does one do that -- observe, perceive, see as a user might?
v3: Beginner's Mind
Last week I read "What Kind of Buddhist was Steve Jobs?", which mentioned, "Apple devices, you might say, are sophisticated tools for evoking, supporting, and sustaining shoshin, beginner’s mind." The article also referenced the Zen quote, "in the beginner's mind there are many possibilities, in the expert's there are few."
That quote is powerful in life, generally, but also for product design, in particular. Beginner's mind is exactly the concept I was looking for; it's a more general, deeper version of what I was getting at with "seeing wide." In Zen, shoshin "refers to having an attitude of openness, eagerness, and lack of preconceptions when studying a subject, even when studying at an advanced level, just as a beginner in that subject would."
Most of the abstractions through which intuitive perceivers perceive are not unique. They're things like "call to action", "left hand nav", "drop-down menu," which are all part of a shared culture. So, in order to make interesting new choices, product designers need to cultivate the ability to look at their own work with beginner's mind--without expectations, without prejudgements, seeing it as it is, versus as abstractions. Only then will interesting, new possibilities be apparent.
One seeming paradox is how to bring to bear your knowledge and wisdom upon a situation while also recognizing that your knowledge and wisdom hold you back, and cause you to see things through a set of distortions that you're not even aware of.
I'll end here. Others are more qualified than me to talk more about shoshin: