I once collected sports cards.
My means to store sports cards were to slip the card into a soft-sleeve cover, whether in a binder or a plastic bin made for card collecting. For "more valuable" cards (ie. rookie cards), I would slip the soft-sleeve covered card into a hard-sleeve cover.
I have taken a look at different grading scales for the condition of sports cards, and one thing seems to be common in card collecting...a card that is graded as "near perfect" is known to be in "mint" condition.
One grading scale grades a card in "mint" condition as a 96/100.
A minor flaw may exist upon close examination.
Another grading scale grades a card in "mint" condition as a 9/10.
...a superb condition card that exhibits only one ... minor [flaw]
What factors should I consider toward keeping sports cards in mint condition?