Buying a bike is just like buying a car for the most part, EXCEPT that you most likely won't be able to test ride the bike before purchase. Most dealers don't allow test rides. Private party sellers won't allow it unless they have purchase cash in hand.
Make sure you have enough money set aside for decent gear - helmet, jacket, gloves, boots at minimum; riding jeans or pants too if possible.
Don't be afraid to ask questions - there's a lot to learn but there's a lot of good info here. Many of the members are quite knowledgeable, heck some of them even know about riding motorcycles, but they can be savages at times (mostly when the weather sucks and can't ride).
Good luck in your search and welcome!