Have available more boxes than you think you will need. Wrap glassware or breakable items in protective material like newspaper, bubblewrap, styro beads etc.
Label all of your boxes with numbers and contents on more than one side. Create a separate written list of all the boxes for future inventory checks.
Never store anything combustible like petroleum products, paint or chemicals. Drain any fluids from lawn, garden or other equipment that is to be stored.
Fill the boxes completely and secure with duct tape to add strength for stacking. For heavy items or taller stacks use plastic totes as opposed to cardboard containers.