Are you shooting film or digital?
The percentage of "keepers" you mention was actually pretty standard with film, even for pros. Getting a couple or a few really good shots a roll, while not exactly a stellar batting average, was always considered good enough for most commercial work.
In the age of digital, however, I think there is little excuse for missing on that many shots, even with a small LCD screen.
What exactly do you find wrong with the shots you feel fail? Is it an exposure thing? Or more the composition?
Not to sound my own horn, but if you check out my recent post on improving your shooting:
<a href="http://forums.photographyreview.com/showthread.php?t=2380" target=_blank>http://forums.photographyreview.com/showthread.php?t=2380</a>, I think you may soon learn to see better and increase your percentage of better shots.
If you can be more specific about your problems, we can give you better advice...