Know where the snake is coming from (shop the breeder thing), find out everything you can about the snake (how and what it eats, health/feeding concerns, gender, age, etc.), do your research first so you know what you can and cannot deal with, set up the housing BEFORE you get the snake and get the best advice possible about how to settle in your snake. Do all that and in the end it doesn't matter whether you get an adult or a well started baby, you should do well (as long as it's not, as previously stated, being sold off because it's a problem adult).