Plaid is a risky pattern to incorporate into window treatments. Often, these curtains can be too busy to fit into a wide swath of design schemes, or have a connotation with masculinity that limits the sort of spaces you would want to use them in. Also, some plaids may seem too casual to fit into more elegant spaces,leading you to avoid the pattern completely in formal settings.
However, when used with the proper colors and materials, a plaid design can make a room pop, incorporating hues used throughout a space to complement other decor.Your plaid curtain will avoid being too loud and actually exude a well thought out elegance by using a palette of colors derived from a specific point on the spectrum.
In a bright dining room, consider a yellow design scheme that bursts with color. A strong yellow wall with a white molding chair rail at waist level can be the basis for your color scheme. Incorporate tans in other places throughout the room, such as with napkins or place settings on the table. Then, choose a drape that incorporates all of these tones into a plaid, and coordinate it with a tablecloth that does the same. Accentuate the curtain using a white sheer to add lightness to the look, then complete the design with yellow flowers as a centerpiece on the dining room table.
You can use this as the basis for any number of color schemes, making it so the curtains doesn't steal the show so much as tie the whole design idea together.