Mobile is not just different screen sizes. Mobile devices actually change the fundamental user experience of common tasks. Embrace the devices and their native capabilities.

Think mobile first
Designing for mobile first is very beneficial even if your main focus is not on mobile. Doing so can help eliminate nonessential information while reinforcing the most important information.
Consider new use cases
What are the scenarios where people will be using your application outside of the traditional desktop environment? Reevaluate the need to have some features and capabilities designed for smaller screens. Take advantage of the capabilities that mobile devices have to offer, such as a camera and notifications, when designing your application.
New devices sizes
Do not plan your designs with a specific and unique resolution in mind. Consider that new devices are launched throughout the year. The more fluid your design is, the better your application will behave, regardless of the resolution and density of the screen.
New device capabilities: GPS, camera, accelerometer, etc.
You can use these new capabilities to implement features that require geopositioning and location. Use the device orientation to provide a different view of the same screen or some related data.
Users become accustomed to gesture support on their platform. Swiping, pinching, zooming, and even multi-finger gestures are becoming commonplace in mobile applications.
Appropriately sized tap targets
A fingertip is less precise than a mouse pointer therefore needs a larger target. When designing for mobile, remember to increase the size of buttons, form elements, and controls.
No hover
Without the capacity to hover on elements on a touch screen, be careful with the type of information or interaction that you associate with this action on the desktop version.
A desktop experience is not a mobile experience
Consider the context in which people will be using your application. Desktop and mobile experiences are far from seamless. For example, if you have a secondary feature that is composed of several steps and interactions, you may leave this experience for the desktop version only.
Selection is preferred over input controls
It is much easier to select a value from a pre-populated list than it is to input a value into a field using a (virtual) keyboard.