The ratio that's reasonable varies dramatically with the subject matter you tackle.

If you're taking pictures of landscapes or flowers (for a couple of examples) it doesn't take a lot of practice to get to something like 2 out of 3 being at least reasonably acceptable.

If you decide you want your flower picture to include (for an obvious example) a bee, that ratio immediately drops drastically -- 1 out of 20 is probably doing quite well, and 1 out of a hundred wouldn't really be any reason for major disappointment.

In general, a subject that's large and fairly slow moving tends to be relatively easy. A subject that's small, shy, fast moving, or (worst) all of the above, can be difficult to capture reasonably at all, not to mention really well.

Innate attractiveness (beauty, cuteness, etc.) of the subject makes a big difference as well. If you start with a sunset, flower, kitten, puppy, baby, beautiful woman, etc., about all you have to do is avoid obvious problems for most people to judge it a good picture. In portraits, the technical quality of the picture is usually much less important than the expression you capture.

If you take a picture of a leaf, tree bark, railroad tracks, old building, etc., your creativity and the technical excellence of the picture become much more critical. With a beautiful subject, a mundane capture can be entirely adequate; with a mundane subject, you need a beautiful capture.