If you haven’t already, you should first form a Game Design Document (GDD), or alternatively, a collection of reference images. An artist has no idea what a client means by a “cool warrior character”, however they can concretely understand a moodboard showing the specific type of armor the character wears, likenesses their appearance is based on, and paintings matching the desired art style. Pinterest, Tumblr, and even Google Drive are widely used tools for compiling and sharing reference material. A good game artist can nail a design in very few iterations, but regardless expect some back-and-forth between you and your artist until you’re satisfied with their work.
If you’re leading a game’s development, it’s up to you to also send any relevant technical information to your artist. Technical information commonly includes things like file formats, image sizes, and engine limitations. If you’re unsure what kinds of technical specs your artist needs… ask!
