#24 Expensive curriculum
Especially if you are new to homeschooling. There are lots of publishers promising to solve all your homeschooling problems, but don't rush to click 'buy"! Most homeschoolers spend the first year (or two) figuring out what approach works best for their family-- because their are so many choices, its very likely that whatever approach you start with will need to be tweaked, and it will be less painful to change if you don't have too much money invested. Even when you've got a few years under your belt, it's wise to avoid curricula that's so expensive you couldn't abandon it if turned out to be a bad fit.
Instead of spending lots of money on curriculum, buy used, borrow from the library and use the internet. If you aren't sure what to buy, ask! Homeschoolers love to talk about what has and hasn't worked for them- listen to their reasons, and then consider your family's needs and preferences. And if you do buy something that doesn't work for you-- sell it! It might be wonderful for someone else, and you'll be able to reinvest the proceeds in something better for your homeschool.