Linens. Pack linens with a few dryer sheets to keep moths away and keep them smelling fresh. Air release bags or suitcases also work well for keeping them safe from water damage.
Delicates. Glass and keepsake ornaments should be kept in their original boxes, if you have them. If not, allow your stockings and linens to do double duty by packing them with fragile ornaments. You may also want to use other linens to pack delicate things - but make sure to put a note at the top of the box so next year you can remember to carefully handle specific stocking or blankets filled with fragile items. For candles and other things that scratch or dent carefully, stick them in old socks. Store all delicate items in a climate-controlled place to avoid heat damage.
The tree. Putting away an artificial tree with the lights still on is the hardest part of the Christmas cleanup, but a few simple steps will help you keep it in a smaller place and preserve it longer. First identify any lights that aren't working and replace them immediately; this will prevent your entire string of lights from burning out. Then un-fluff the tree by folding baby branches back to the big branches. (This step is commonly skipped, but it protects the needles, branches, and lights better.) Carefully wrap and tie the tree in a plastic bag.
Inventory. With your boxes already labeled, make a list of the things that went into each box. Keep this somewhere you'll remember it (like in box #1) so you can easily find items next year.