A mint card stored badly is a near-mint card in six months. If you're spending real money on singles or pulling chase cards out of sealed product, your storage strategy matters more than most people think.
The basic stack
Every card worth keeping goes into a penny sleeve, then a perfect-fit sleeve, then a top-loader or semi-rigid. That triple layer is what protects edges and corners while you decide whether to grade.
For long-term storage, keep cards out of direct sunlight and away from radiators. UK lofts and garages swing wildly in humidity — both are terrible for cardboard.
Which grading service?
PSA is widely considered the resale benchmark, especially on Pokémon. CGC has grown on the back of faster turnarounds, and BGS retains a following for Magic singles. Pick based on what you're grading and how quickly you want it back — and check recent sold prices for the specific card and grade before committing.