The biggest mistake first-time homebuyers make

If you're planning to buy a home, you should be ready to spend some serious cash.

In addition to putting as much as 20 percent down, you also need to have enough in the bank to cover closing costs, moving expenses, repairs and the first few months' mortgage payments, all without draining your emergency fund.

Home buyers must also make high-stakes decisions about their budgets, ideal location and what they're willing to sacrifice if the price is right.

For first-time buyers especially, navigating this landscape can be overwhelming, so it's natural to retreat into what's comfortable and known. And that's where you can slip up.

A couple look at houses for sale in the window of William H. Brown estate agents.

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Setting your sights on an ideal neighborhood or specific amenities could be detrimental to the process. In fact, the biggest mistake first-time home buyers make is not keeping an open mind, says Cathy Derus, CPA and founder of Brightwater Financial.

Having recently bought a home in Chicago herself, Derus knows that every city has neighborhoods that are popular, well-established or trendy. But it's not wise to settle on a certain area before considering others.

"Work with your realtor," Derus tells CNBC. "They might have some suggestions of other areas that might have that similar feel to what you're going for. Some lesser-known areas still might meet your earlier requirements, [but] might be a little bit more affordable."

Don't default to what's familiar or easy. Make the choices that make sense for you. As she puts it, "Be intentional with your purchase."

Derus explains that it's also important to keep an open mind in terms of what you're looking for in a house itself. While there's nothing wrong with dreams of a big, beautiful, newly-renovated space, sometimes a fixer-upper offers the right price in the right place.

She says that, while you need to be honest about the types of DIY projects you can take on, it's often worth it to "buy a home that needs a little bit more work so that you can personalize it yourself."

You don't want to blow your budget because you're fixated on small details that could be added or updated later, such as granite counter-tops.

"It might make more sense over time to do some of those projects yourself," Derus says.

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