Before you buy a cell phone, a dishwasher or a new computer you talk to friends, read reports, comparison shop. But do you invest the same amount of time and preparation in furniture shopping? After all, a good sofa or dining table will cost more than those items and will usually last longer.

I asked designers, salespeople and industry experts to describe the most common mistakes furniture shoppers make. Here's a summary of their responses, along with tips on how to avoid becoming a victim.

Lack of Preparation

People often go furniture shopping without any sense of what they like, their long-term goals, or even something so basic as the dimensions of the room. Before you visit your first store, draw up a floor plan of the space you’re shopping for, including all measurements. Take some photographs of the room, and go through design magazines and tear out photos of homes or furniture pieces that appeal to you. Bring paint samples from the room, along with swatches of carpet and fabric from the other furnishings. If you don’t have a fabric swatch, remove the cover from a cushion and bring it with you. Pack these clippings in a file folder or portfolio and bring it with you when you shop.

Think about your long-term plans for the room: Do you like it the way it is, or do you want to change it? If it’s the latter, what kind of look or feeling do you want the space to have? Buy for the way you want the room to be, not necessarily the way it is; that way, you’re not tossing out your furniture in three years when you finally get around to decorating it the way you want it.