Stick to a Color Scheme
One approach for interior design is to start with a color scheme. You have the main color and a couple of accent colors. As an accent item, your new mirror might be an excellent choice for one of the secondary colors. Peruse the frames the shop has available, and look for one within your accent color. The frame doesn't have to be the exact color from your palette - a shade or wash could look attractive.
Stay Within a Décor Style
Similarly, perhaps you've chosen a specific décor style for your room. Your mirror frame should fit within that style. For example, if you're going for a glamorous ambiance, consider an elaborate and even gilded frame. A distressed frame would be charming in a cottage or shabby chic room. An unstained wooden frame complements rustic and country décor.
Indeed, the purchase of a custom mirror is ideal for this situation. Research the style ahead of time. Look especially at framed mirrors and even framed pictures in your target style for inspiration.
Aim for Balance
When you decorate, your pieces should have a sense of balance, which comes from their scale and proportion. So, the frame should have an even balance with the rest of the décor. For instance, an oversized frame works well to balance another visually heavy item, such as the sofa. The mirror and its frame need to work within the scale of the room, too, to maintain that balance.
Add Pattern or Texture
You can also take another approach to achieve that visual balance. Frames with patterning carry visual weight. The pattern can come from paint, cutouts or even tile. The frame itself may be perfectly scaled to the mirror, but will still draw the eye because of that pattern.
Texture can have a similar effect. With texture, the frame finish will probably be consistent, but you'll see three-dimensional patterning in the body. A textured frame is probably more subtle than a pattern.
Match with Metal Finishes
Textured frames often feature a metal finish, but you can find smooth metal frames, too. If you're considering a metal frame, look around for other metal finishes in the rest of your décor. The mirror frame doesn't have to match those finishes exactly. However, you want to show some cohesion. For example, if you already have some silver, look for a metal frame with silver undertones.
Make a Statement
When you choose a custom mirror, you might want it to be the center of attention. Mirror glass alone would have difficulty providing the focal point of your décor. A big, bold frame, however, would draw attention to your new mirror.
You have many options for how to make that statement. A wide frame will draw attention, as will a boldly colored one. You could also look into some of the more elaborate styles, such as those with a lot of trim or even one made of more mirrors.
Try a Minimalist Approach
Perhaps you don't plan to buy just one custom mirror but several because you want to make a gallery wall or art installation. In that case, consider minimalist frames. These are usually simple beveled styles with a subtle profile. If you chose black frames, this approach would be very chic. A minimalist frame also looks good on a single large or oddly-shaped mirror.