There are many misconceptions about the one sheet that should always be included in a promotional kit.
I've heard it described as a brag sheet, which is incorrect.
The main purpose for the one sheet is, and always has been, intended for retail and radio outlets artists are targeting for sales and airplay. To that end information relevant to retailers and radio programmers is essential.
The best example I've seen recently of an indie produced one sheet can be found here http://brittnipaiva.com/
Follow this example to a "T" with compelling colors, graphics, photos, etc. that truly highlight music you are promoting. Be certain the information is accurate, complete, easy to read, and understand.