Imagine the world's attention as a big foggy cloud. So thick you could cut it with a knife.
You want to cut through that foggy cloud, to call attention to your music.
Only problem is, if you're well-rounded, you can't cut through anything. You need to be sharp as a knife. Sharply defined.
Example: Your name is Mary and you put out an album called “My Songs”, and the cover is a picture of your face. The music is good quality, songs about your life, and when people ask what kind of music you do, you say “Oh, everything. All styles.” You send the album out to be reviewed and nothing much happens. Doors aren't opening.
Imagine instead: Your name is Mary and you write 9 songs about food. You put out an album called “Sushi, Souffle, and Seven Other Songs about Food”. Maybe you recorded your vocals in the kitchen. Maybe you quit cooking school to be a musician. Yes it's a silly example, you see how this would be MUCH easier to promote.
You may be thinking, “But I have so much to offer the world, I can't just limit myself like that!” If you want to increase your chances of the world hearing your music at all, though, strongly consider stretching-out your musicial offerings to the world, and keeping each album focused clearly on one aspect of your music.
Notice the long careers of David Bowie, Madonna, Miles Davis, Paul Simon, and Elvis Costello to name a few. Each went through sharply-defined phases, treating each album as a project with a defined mission.
Here's some top-sellers at CD Baby:
Eileen Quinn. She's a full-time sailor. She writes songs about sailing. That's it. Five albums of them. And sailors LOVE it. She gets written-up in sailing magazines all the time.
Rondellus. Sabbatum. A traditional medieval music group from Estonia doing an album of Black Sabbath songs played on medieval instruments and sung in Latin.
4th25. American soldiers in Iraq wrote and recorded an album in their barracks on a cheap computer with a $100 mic, about what it's like to be over there at war.
Each of these albums got a LOT of press and a lot of sales, because they were sharply-defined, newsworthy, interesting to write about, easy to tell friends about.