And, finally, if you want to do some usability experiments and testing:
Look at a LOT of good designs & try to incorporate elements into your work. https://dribbble.com/
When you work with a standardized set of UI elements on a canvas of limited size, you tend to start thinking about the interface in terms of modular actions and tasks, which you can repurpose later when scaling up to tablet or desktop web. You also have a good basis to simplify these tasks further when branching out to wearables and in-car devices.
At this point, Google, Apple, and Microsoft each have pretty defined ideologies and UI — check out their guidelines:
Check out some of the sessions from WWDC and Google I/O too:
There are also a lot of great blogs out there that have pinpointed info on different parts of interface design. Sometimes these info-morsels can be easier to digest than starting a full course in UX. This is definitely not a comprehensive list, so look around, and get your RSS client fired up.
Luke W's notes from conferences are usually pretty informative, and he has articles going back to the early 2000's, for extra perspective.
If you want info on actual implementation, at least in Photoshop, you can't do better than usTwo's Pixel Perfect Precision handbook and Marc Edwards' articles: