First, get to know your rights. Check on your employer's policies regarding maternity leave. You also need to read up on your legal rights.
Secondly, ask someone you trust, possibly a co-worker or colleague who has been on leave recently. Ask her how she was treated during her pregnancy and how her leave was handled. Can she share any other helpful information with you?
Thirdly, think about how much time you want to take, when you want to start the leave, do you plan to be accessible to work once you have started your leave, how you wish to return to work – full time, part time, flexible schedule, or telecommute, and who will handle your responsibilities in your absence.
Fourthly, set up a meeting with your boss to discuss your situation and plans. Be sure to formalise all the arrangements you agreed upon in writing, and send a copy to human resources, so that there are no misunderstandings in the future.
Fifth, be prepared for surprises. Even the best made plans can go awry. Babies tend to arrive on their own time schedule. You could have unexpected complications. Keep these in mind when you are considering the time your leave will begin and end.
Sixth, never assume that just anyone can do your job, and do it as well as you do. Make sure that your replacement can handle your clients, reports, subordinates and other responsibilities. Leave them step by step instructions and your contact information.
Seventh, set some boundaries before you leave. If you wish to be kept up to date with what's happening at work, request daily or weekly outlines to be sent via email. But on the other hand, if you only wish to be contacted in an emergency situation, then politely say so.