Dimensions in UI.

Light mastery in design is one of the most important things to learn when learning UI Design. It definitely helps when you think of your objects as a real 3D “stuff” that you can play and interact with, to see how they react to the properties of light.

Imagine if you could get a cursor or touch a button, what would be your object under a light source? How would it be under two light sources? What we see on a 2D screen must have the same properties under real conditions.
My advice to anyone starting to learn Design is to pay attention to the amounts of light as well as the amounts of shadows in their prototypes.

When you think of a shadow, think of light.

Shadows are valuable cues that tell the human brain what elements we are looking at. For example, if you have a text with a shadow, then it is implied that there is a light source somewhere which in turn should have a universal influence on the rest of the elements, e.g. buttons or infoboxes.
If there is are shadows, there is light.
So pay attention when combining different lengths and distances of shadows, to avoid discontinuities and logical incompatibilities, and do not hesitate to use them.

Think your workflow through

Flat design is known for its lack of depth. There are no shadows, the highlighting of objects may be in the form of borders or gradients, which it is basically like taking your objects and squeezing them under a hydraulic press. Flat design should not be a refuge for lazy designers, a great design needs careful thought, a sophisticated plan and most of all strategy.
As technology evolves, so do design trends. We are starting to see a great return to skeuomorphism and animation in the UI, and there is a growing trend in designs width depth and perspective.