Columbians are known for their mellow personality. That said, there are exceptions as personalities differ from snake to snake. I would buy from a breeder who handles their snakes and I know of two: Sharon Moore and Jimi Reed. Jimi has a ton of good choices and Sharon breeds mostly normals.
Columbians are also more forgiving with husbandry issues than other locales of Bci's. Stay away from all Bcc's as they require more knowledge than a first time boa owner has.
Be prepared to have a large cage in the ready. Mine will move into their 6 ft cages when they are about 2 years- maybe less. Until then, they are in their 2x3 RBI cages. I also have RHP's in each cage.
For a large snake there is a 6 foot safety rule: For each 6' of snake there is one handler. As soon as your snake is over 6', you need to have an assist handler helping. This is for the snake's comfort as much as is for your safety.
The rest is common sense stuff that Wes already mentioned: don't smell like food, get to know your snake by handling often, learn to read your snake's moods.

Boas are amazing animals and I recommend them for anyone looking to buy a large snake. Feel free to PM me for anything else if you want.
Take care.