Concept Design

Concept Design is a form of an illustration, main goal is to show an idea, which usually will be useful for movies, games, comics etc.
Concept artists're using different styles, some of them start in a traditional way, the others are pure digital.
As a concept artist one of the most important thing is speed, sometimes You need to deliver a lot of concepts per day.
The most common tools for digital painting are graphic tablet+photoshop or corel painter
(some people like free Gimp)
A lot of people are wondering, what is the difference between illustrator and concept artist?
Well, illustrator sells own finished paintings, concept artist sells ideas, which can be finished by someone else.
Check this site:

http://www.fzdschool.com/ent_started.html

and

Fengu Zhu one of the concept artists tell about it in a nice way.
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Few things I would like to recommend:

• observing the world (a lot of things around us can be an inspiration)
• reading the books (You'll train your imagination)
• fundamentals (not only perspective, shadows,lights, colors,composition but also how things work in a real world, if You're designing a car try to read about them and search a lot of references in this way your design will be believable)
• anatomy (it's "must" if You want to create a characters)
• graphic tablet (most common is Wacom)
• graphic software (photoshop, corel painter, gimp etc.)
• practice, practice, practice (if You'll practice a lot, the only thing that can stop You, will be only your own imagination)