Label and Index
Of course, if you've got a lot of bins, you've got to have a way to keep track of what's in them. Labeling can help. Try placing an index card on the outside of each holiday box. Include on the card what holiday the box is for, as well as its general category: "Easter -- Decorations," or "Christmas -- Ornaments," for example. Include a few bullet points on the index card about the general contents.
Another approach is to number each box (i.e., Halloween 1, Halloween 2, Halloween 3, etc). Then, write down everything that's in each box and create a document on your computer or a file of index cards that lists the complete contents of each box.
One more labeling tip: For each holiday, designate a certain box to be the "open first" box. This will help ensure that you kick things off in a logical way. For example, you probably wouldn't want to open the tree skirt box if the tree box hasn't been opened yet.