Quick answer
Sleeve cards before putting them in rigid holders, choose a box that fits the holder you actually use, and keep the collection in a stable, dry place away from direct sunlight.
Sort first, then choose the holder
Separate base cards, cards you handle often, and cards you want to protect more carefully. A sleeve and a correctly sized storage box can be enough for bulk base cards. Use a sleeve plus a rigid holder for cards you trade, ship or display.
Sort by set and card number if you complete checklists, or by player and team if you collect a few names. Label the outside of each box and use dividers so you can find a card without repeatedly handling the whole stack.
Match the box to the card and its holder
A standard cardboard card box is meant for loose or sleeved cards. Many ordinary card boxes are too narrow for top loaders, magnetic holders or graded slabs. Measure your actual holder before buying a box, and check the manufacturer’s interior dimensions rather than trusting its headline card count.
For example, BCW describes its 800-count box as suitable for loose and sleeved standard cards, but not for top loaders or slabs. The stated count also varies with card thickness and sleeves.
Keep the environment steady
Store boxes on a shelf rather than directly on a floor where leaks can reach them. Avoid direct sunlight and damp or fluctuating spaces. A sleeve or holder reduces handling damage, but it does not make a card waterproof or eliminate heat and light exposure.
Keep food and drinks away from the sorting area. Handle cards with clean, dry hands and support the edges. If a card feels tight in a holder, stop and use a holder designed for thicker stock.
Choose binders for browsing, boxes for density
Binders make a full set or team collection easy to browse. Use pages designed for the size and thickness of your cards and avoid overfilling pockets. Boxes use less shelf space and make it easier to keep many sleeved cards in order.
For a mixed soccer collection, a useful split is a binder for the set you are building, labeled boxes for bulk, and appropriately sized rigid holders for your favorite rookies, autographs and numbered cards.
Sources and product specifications
Check the maker or grader's live page before buying a holder or submitting a card. Specifications and service terms can change.