I just got my snake done on my back, best thing to do is pick out the type of boa you really like. And what else you want into the tattoo, if you want the snake VERY realistic it's going to be a big tattoo because it's hard to get that much detail into something small. I tried that, didn't work out how I wanted but I still like it. Make it your own custom tattoo, find yourself a good artist and do some re-search on him before just going to him.

Take all your ideas, and talk about what you like and how you want it to look and if the artist is able he should put it together just how you like it.