My advice would be to think it over a long long time. If you haven't decided on a specific tattoo and been happy with that idea for 6 months, I wouldn't get it personally.
I have two, and have one other planned. 6 months ago I had 3 planned. I'm tentative about getting a ball python one, but it's probaly going to get done at some point.
A tattoo should be a personal thing and is a permanant addition to your body. A half sleeve(or possibly quarter sleeve which might be what you mean too) is a lot to get put on you to decide later you don't like it. It's hard to cover up withs omething else later too.
Myself, I'm all for original art that means something to the wearer. Both of mine were all orignal, and have deep meaning. With traditional art, the koi and the dragons are seen a lot because they always look good.
Snakes can be hit or miss, it depends on the artist. I'm not a fan of most of the demons, skulls and such, so I couldn't advise you on those.
Wolfy