So to get this one going let's just lay down some ground rules.
A) While the colour options for metro tiles are infinite, I am using the most commonly used as the basis for this blog - white.
B) There is a difference, believe it or not, between metro/subway tiles and rectangular tiles. Whilst metro tiles are rectangular, I hate to break it to you, not all rectangular tiles are metro.
Now I know that this blog isn't meant to be a lesson in etymology, but I feel that it's important that we get this right. Metro tiles, used in the first New York subway station in 1904, were 3x6 inches. That's roughly 7.5x15cm for those of us that use the metric system. Unfortunately over the years the term has somehow morphed to include any small tile that isn't square, a fact not helped by the the varying array of tiles used on the London underground.
Now I understand that you may be sitting there thinking that this is all just semantics, and that "a rose by any other name will still smell as sweet" however you are wrong. The correct proportion of a metro tile is vital, which leads me to the first point.
1) If the tile isn't either 7.5x15cm or 10x20cm its not a metro tile. So if you are after that subway look make sure you pick the right tile to start with, or run the risk of a kitchen or bathroom that reads less "Grand Central" and more "end of the Central."
2) Unless your tiler can walk on water and later turn that water into wine, try and avoid a bevelled* metro in a space that has loads of corners or junctions. So in a shower or bath enclosure for example. If the walls are skew and the tiler is anything but a master-craftsman, it all starts to go wrong. Bevelled tiles don't do well when two cut pieces have to butt up in a corner. Unsurprisingly this is a common scenario in the likes of a shower. So rule of thumb, flat wall-to-wall areas, a bevel is perfectly fine. Lots of corners and junctions, rather opt for a tile without a bevelled edge.
*A bevelled metro tile is one where the sides slope up slightly, and give the look of a block of chocolate when grouped.
3) Following on from this, dark grout is very seldom your mate. If the tiling isn't perfect, dark grout against a white tile is the equivalent of your worst enemy standing next to you on a first date pointing out all your flaws. Guaranteed you will not walk away getting lucky. I'm not saying you have to go with light grout each time, but the darker you go the more obvious the awkward tile cuts or errors become.
4) If you want to use a darker grout however, use your wall colour to determine the shade you use. Generally the darker the walls adjacent to the tiles, the darker grout you can use.
5) I am all for mixing it up when it comes to how you want to pattern your tile, but if we are all on board with the true sizes of a metro tile, not all patterns work. Below are the patterns I think work best...anything else starts to detract from the true look of a subway.
Brick Bond | Vertical Block | Horizontal Block
6) Metro tiles are like a school of fish; most visually impactful and beautiful in large numbers. Now I know that budget might come into play when deciding how much of a wall to tile, but try to keep the use of metro tiles to large quantities, covering floor to ceiling or the full width of a wall, rather than sad little groupings that stop and start their way around a room. To put it simply, using six metro tiles as a splashback above a pedestal basin is like a single trout flapping on a muddy shore...a little bit sad.
(That above goes for all tiles really...you never want to see more that one edge of a tile)
7) In a previous post #gotbush, I mentioned that if your house plants become the main focal point of a room, it might be time to ask what your interior is really lacking. Something similar could be said of metro tiles. These guys shouldn't be the star attraction in a room. They are the Prime Minister's husband or wife, there to support but not steal the show. So bear this in mind if it starts to feel like they are creeping into the spot light or drawing too much attention to themselves.
8) Finally, not all metro tiles were created equal. Just because it says "white" on the box, doesn't mean they will automatically match the other white finishes in the room. Get a sample before you buy a whole rooms worth. There may be 50 shades of grey, but there are literally quadruple that when it comes to white.