Specific and Distinct — "I want to play basketball" isn't enough. What position do they want to play? What got them interested? And maybe that's not enough. Plenty of people want to play basketball. What makes this particular desire specific to your character? They must answer the all-important question, "Yeah? But why should I care?"

Real — If these desires or details or bits of history feel generic, unimportant, or unrelated to your character, you've lost readers. If they can apply to just any old cookie-cutter character, they're no good. Why this character? Why is this important to this singular, distinct human being? Why does it matter to them, and how does it intertwine with their needs and desires?

Memorable — If you mention it once on page one and then it comes in on the last page and you want it to make a splash, good luck. (I mean, if your story is two pages, you've done well, but otherwise, be careful.) These callbacks and details should be inextricable from who your character is. Maybe you don't mention it again in words, but readers recognize it in the way the character counts how many quarters she has in a jar or in the way he runs every morning until his feet blister. The characters don't have to say a word, but you know it. You see them striving, and it matters. Don't ever give readers a chance to say, "Wait... what? Why was that important again?"