I saw an article that recommended folding on the bias (diagonal) rather than the more common square folding. Folding on the diagonal places less stress on the fold line; a bias fold is stronger because there are many individual threads taking the fold. When you fold on the straight-of-grain, only a few threads are taking the stress of the fold.
It's also a good idea to purchase archival-quality tissue paper. Wood products (including paper and cardboard) contain wood acids that can discolor and eventually eat holes in fabric. Archival quality paper and cardboard have been processed to eliminate the acid. (This applies to storage of photographs in albums too!) Ball up the tissue paper and place it in all of the folds so the folds are rounded rather than sharp. This also relieves stress on the folds.
The folded quilt can be stored inside a clean pillowcase or achival-quality cardboard box. Never store a quilt in direct contact with wood (as in a cedar chest) because of the acids in wood. Always keep a quilt away from sunlight and also artificial light (including flourescents). Light of any kind fades fabric. If you take the quilt out for display, be sure to display it out of direct sunlight.
Even with diagonal folds, it is a good idea to re-fold the quilt (along different lines) every 6 months or so to avoid permanent fold lines.
There are other ways to store quilts too. Perhaps the best is if you have a spare room with a large bed. The kindest way to store a quilt is flat on a bed, covered with a sheet or two to keep light and dust off. Several can be stored this way, with a sheet in-between each. Museums store quilts like this on pull-out shelves in temperature and humidity-controlled rooms. People handling those quilts always wear white gloves to avoid getting skin oils and sweat on the fabric.