In most stories, we know enough about the main character to portray them in a way the reader can understand. We should know what they basically look like, their basic height and weight, and any stand-out features they might have - a limp, freakishly large hands, eyes of different colors, etc. Once I lay out these details, I have the basic character - the 5'11", 220-pound, brown-haired, blue-eyed, balding guy with a shuffle to his step and evidence of a history of broken noses. He is drawn-out. He exists. He is real.
And frankly, he is boring.
Boring? Not the best way to describe a main character (and since this is also a bang-on description of me, it's definitely an unusual choice). I mean, there's nothing wrong with that description, and it is something the reader can immediately understand. However, the description is little more than a report about the character's appearance. None of that description really does anything, and in this regard, it's boring - not the best main character to have.Now, am I suggesting that a main character, therefore, has to be 6'9", a svelte 310 pounds, freakishly blond hair with black streaks, red eyes and a brutal scar across his cheeks? Well, you would remember that visual, but that character might not fit the story very well, especially if the story was about a middle-aged writer contending with his mortality. Rather, you need to take the elements of the character and make them stand out in a memorable way, so that the 5'10" person has a more engaging description. One way to do this is to think of the old art of the caricature.
We think of the usual caricature as something we get from some guy with an easel out on Navy Pier. For $10 he draws a real exaggerated sketch of you, making a few features stand out dramatically. The portrait of you usually includes having your head's proportion to your body similar to Charlie Brown, your expression expanded to utter joy, merriment, or something else incredibly positive, and usually posed with some dramatic gesture or with a prop as oversized as your now-humongous head. It works; it makes a statement and you get a chuckle out of it. However, the important part is that you remember those key exaggerated points.
A character should be no different in their description, even if they retain normal human body proportions. Look at our writer example. Describing him as 5'11" is accurate but clinical; making him "a boringly average height" loses the detail but adds to the dimension of the character. Instead of citing his weight, suggest he "could afford to miss a few meals" and now the reader starts painting his own picture. Is he balding, or are the last few proud follicles of a once-proud head of thick brown hair stuck on his broadening scalp in a desperate comb-over? Do we need to state he has a limp, or is it better to mention this as a part of his actions? "He walked to the deli, his left leg slow to keep up" gives description as an action, keeping the story moving while offering the reader details along the way.
These tricks take a boring -looking character and make them interesting in the sense that they have depth and dimension. If you want to make your character stand out with freakish height or other aspects, well, that's your call. However, even with a stand-out character, they become recognizable when their description is emphasized and engaged with, even exaggerated, to make the point stand out. They don't need to be fully-misshapen caricatures, but emphasizing their key points will connect the reader to even the most boring middle-aged writer.