I don't mean getting mentally prepared, although if you haven't looked under your sofa in a long time, you might need to be ready for anything when you pull that sucker out. I'm talking about making sure that you have all of the supplies you need. Spring cleaning isn't the most thrilling thing in the world, but it will be even more annoying if you have to stop and run to the store because you're out of something.
You probably have the basics already, but at a minimum, you'll need an all-purpose cleaner for everything from walls to floors and a glass cleaner for windows and mirrors. Don't forget about specialized cleaners, like oven cleaner, silver polish or wood oil, because you probably don't use those things nearly as much. Your tools are just as important: Inspect everything from brooms to mops, and replace them if they're in bad shape. A frayed broom can make sweeping take twice as long.
Spring is also a good time to go green. You can even go one step further and discover new uses for household items like white vinegar and baking soda. You may not have them in the quantities you'll need for cleaning, but buying them will cost you much less than traditional cleaning supplies. Try to avoid using paper towels if you can (although I can tell you that coffee filters are the best way to a streak-free window). Microfiber cloths are great for dusting, and you can use the inexpensive white cloths known as bar mops for just about everything. I use these, as well as a mop with a refillable head that can be machine washed.