A couple of tips.
First of all, it does show you how close you can get with a screw on diopter lens. They don't give the sharpest photos, but they will get you closer than with the lens alone. Get a book on closeup photography (John Shaw's are the best) and read about other ways to get close. There are several other options that don't require you to shell out for expensive macro lenses. An extension tube could really help you for not much money.
As for your technique of focusing then moving the camera back and forth to get focus - that's the best way to maximize magnification.
The only thing I would suggest is to get lower. You are too far above the snake to have captured the snake's personality. Get down at eye level or just above it and take the same picture (from the front of the snake) and you will be amazed at the "pop" the picture will have.
The real key to improving is to be a harsh critic. Look carefully at your pic and decide what you do and don't like about it. Then figure out how to repeat the good things and correct the bad things in the future. Do the same with other people's photographs as well (except mine of course
- LOL).
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Chris Harrison