Find the right doctor for you
Twin pregnancies are slightly more risky than singleton pregnancies, and will require more prenatal appointments and closer monitoring. If you are expecting higher-oder multiples, that is definitely even more important. Finding the right doctor or group of doctors will help you enormously.
Don't go for the first one you find, unless he or she is really great. Ask plenty of questions, specifically relating to their experience with twins or multiples and how they view such pregnancies. Some doctors may like to push "selective reduction" for high-order multiples. If you are not comfortable with that, you should look for a doctor who is comfortable with pregnancies with lots of babies.
Likewise, if you have a doctor who very much holds the view that c-sections are always best for twins and multiples, but you would love to try for a vaginal delivery, there might be trouble. Philosophical differences between you and your doctor do matter.
Read, read, read!
Read books about twin and multiple pregnancies. Read about promoting a healthy pregnancy for multiples, and about others' experiences, online. Read books about parenting twins, and look for threads on message boards about items to get for twins. Look for a support group for twins and multiples in your area too, if there is one and you feel you would like to get involved.
Having more than one newborn at once causes some logistical challenges. Preparing well helps with these. Is there any way you can get help during the newborn stage? Think of things like frozen meals prepared during pregnancy, a house help, or relatives and friends helping you with the babies. These things are especially important during the immediate postpartum period, when your body is recovering from childbirth and you are feeling exhausted.