Another is try and describe something for the first time to a hyper-inquisitive five year old. Employ all five senses and all six thought-processes and how that effects all motives independently.
-Then figure out how to write that as concisely as possible without any loss in detail.

Second and third time around you can trim those details.

When introducing a character, it is often necessary to figure out how that character ended up where they are. Depending on the sort of story, you may feel the need to omit explaining their entire life's story, but generally it's better to have more detail than less. At least until you get a feel for what sort of overly-long lengths of prose are tiresome to your readers. Spoiler-tabs are a nice way to compromise, but are only a crutch for good writing.

Anything "average" should generally be left up to the reader whenever possible. Just keep in mind, "average" is as defined by your partner's ideals and expectations, not yours.

-One case of this nearly breaking-down in an RP was a misunderstanding on the relative sizes of dragons and giants.

-Or mechs and dismounted footsoldiers (infinite Stratos has a wierd scale, and are comparable to Archwings)