A small bathroom at my parents' house became "The Watermelon Bathroom" thanks to a watercolor painting of a Middle Eastern fruit merchant.

They started purchasing some quirky watermelon-themed items to complement this piece, like a vintage watermelon stand sign and a wooden sculpture of a mostly devoured watermelon rind. Anything that didn't fit the theme soon disappeared; eventually, the entire bathroom had been painted pink and populated with watermelon décor.

A theme can help bring more focus to a room and highlight your personal tastes. It can also assist with a more minimalist lifestyle; after all, you won't want to buy new items that clash with a theme, or overstuff a balanced room with new things.

Choosing a theme might go hand-in-hand with selecting a style for a room. Coral Nafie, writing for the home design site The Spruce, says there are overarching styles to consider, such as a casual space designed to be warm and inviting or a more formal area that conveys a greater sense of elegance and symmetry. A style may also be inspired by a certain part of the globe, like a Tuscan style kitchen with earth tones, copper pots, and open cupboards.

The right color scheme can be an important for supporting a style or theme. The home décor site Curated Interior says coastal themes naturally feature blues and greens, while the Scandinavian style relies on black, white, and neutral gray tones.

Don't rush the selection process. Alex Ion, writing for the interior design site Freshome, says you'll want to pick a theme that you can truly enjoy. Otherwise you may start to purchase furniture, artwork, and other items at considerable expense, only to that you aren't satisfied with the new look.

While the theme can be anything you decide, you may want to have it complement the home's surroundings. This will make it easier to shop locally for home décor locally, since area shops are likely to feature items related to a community's natural features. For example, you may go with a beach or nautical theme if you live near the ocean, or focus on a mountain or rustic farmhouse theme if you live in a more rural area.

Take accurate measurements of a room. Curated Interior says these measurements will let you know if a piece of furniture or artwork is too big for the space where you'd like to place it. You'll also need to consider how such pieces will be arranged and make sure the room won't feel too crowded.

Come up with a budget for organizing the theme. You may be able to keep the project affordable by outfitting the room gradually over time, though you also don't want a space to look too sparsely decorated in the interim. Ion says it can help to choose a theme that lets you decorate a room quickly without exceeding your budget.

A theme shouldn't overwhelm a room. Curated Interior says living room furniture should be arranged around a focal point, such as a fireplace or television, and have enough space to allow people to move through the room easily. Many things supporting a theme will be accent items, such as coffee table books or mantle displays. However, what you choose to display on a bookshelf or wall will also play an important role in establishing a theme.

The bedroom should be a calming space, but can also serve as a place to experiment with your personal tastes. Marina Resto, also writing for Freshome, says a rustic country theme is a good option since it helps provide a relaxing atmosphere. However, you can also bring in bolder colors and more unusual items, since the bedroom is a private space that visitors typically won't see.

Small accessories can have a big impact on a theme in a bathroom. The interior design site Homedit says functional items such as a toothbrush holder, shower curtains, and soap dish can all align around a common idea. Wall art will also have a significant effect.