Focus on finish.
Polished or honed? It's a matter of personal preference. Polished marble is glossy and smooth to the touch, but can be slippery when wet. Honed marble is more matte and is better for floors since it offers better traction. It is also a popular choice for vintage-inspired designs. Both finishes need to be sealed regularly to help withstand staining and etching. Honed marble is slightly more porous than polished marble; however, scratches can also be more easily buffed out.
Stretch your budget.
If budget won't allow for an entire marble floor, use a smaller application to create the illusion of a rug on your floor or in your shower to get an elegant look for less.
Look for book-matched slabs (slabs cut from the same piece of stone but polished on opposite sides). When these slabs are placed side by side, they are a near mirror image of each other allowing a fabricator to easily match up the veining to create one unbroken pattern. This is best for kitchen island applications or when using a type of marble with heavy veining, such as Calacatta. Running the veining in the same direction prevents a choppy, frenetic look.
Huge expanses of marble can sometimes feel cold and unwelcoming. To avoid the mausoleum effect, consider using border tiles to define zones, such as vanity and tub areas in a bath.
Vary the scale.
When mixing or combining different stone patterns, be sure to vary the scale -- a large border with smaller mosaic tiles, for example -- so that the patterns don't compete with each other.