If you already have an ob-gyn whom you like and are comfortable with, just schedule an appointment. If you're new to the area or aren't crazy about your practitioner, you'll want to find someone new. Ask friends and co-workers for recommendations, and check out online reviews.
In either situation, it's important to make sure that your doctor accepts your insurance policy. You'll be making lots of visits over the next several months, including pricy blood work, lab tests, and exams, so you'll absolutely want to be covered.