This is really not at all bad, especially for a "grab" shot with a short lens.
I have been working on trying to get a good pic of hummers for over a year. They are so tiny, and move so fast it is difficult. On top of that, lighting is usually challenging.
Since you have hummers, try a feeder or three, add a feeder with just water in it too get a good tripod and a chair with a long good (L) lens and wait for them to show up. Beyond that, just shoot, and expect a lot of non-keepers.
You may also want to try a Cam Ranger for this. Add light (flash) or change camera position as needed. I would recommend a high shutter speed to freeze wings- say 1/1000 or so, maybe higher if you have the light for it.
So my wife and I were walking in the park and she spots this hummingbird and points it to me. I have never seen one before, and got quite excited and worked up. The results were quite dismal (the best effort is below), so I am not even going to ask what I did wrong. But let's say this situation arises again, what should I do to ensure at least optimal results. I had a 135mm L attached to my 5dIII, ISO 160 (was set on Auto), f/8, 1/125 (was set on Av, forgot to change it in the haste). Thanks in advance.