Shooting black and white landscapes requires slightly more thought than you might think. A fundamental part of black and white images is separation between the key elements in the image. Without this, the image will look flat and not very pleasing to the eye. An image lacking separation will lack impact and the viewer might struggle to understand it, especially if there's a lot of areas of the shot that have similar tones. This is especially true when an image is converted from colour to black and white, as the tones in the colour image may not easily translate into a mono shot.
One way to stop this is with a strong composition as this can help separate the elements within the shot even if they have a similar tone. Strong foreground interest is particularly important and as photographer Robin Whalley said in a previous article, so are strong distinctive shapes: "Seek out strong shapes in the landscape such as walls and trees that might provide a leading line into the landscape. Strong distinctive shapes are easier for the eye to pick out and understand even when the tones are similar."
Even though many cameras, including the Olympus OM-D E-M10, now have a black & white shooting option built-in, for more control over your black & white images open your colour shots up in editing software and convert them to black & white.
As Robin Whalley pointed out previously: "Ideally you need a conversion technique that allows you to target different colours so they appear as different tones in the final image. For example, you might darken a blue sky whilst lightening grass and foliage."
Boosting contrast by applying an S-Curve to your images will help areas of the shot become more distinct, or if you've shot in RAW and are using RAW conversion software you can adjust midtone contrast with the Clarity slider. Another option would be to use the Dodge & Burn tools in Photoshop to selectively darken and highlight areas of the shot.
For more information on Robin Whalley, take a look at his blog.