My twins are 10 years old. I was excited, nervous, all of the above when I found out from day 1. It is amazing, wonderful, and a very special thing to have twins. First, if you have a supportive partner/spouse, parent, friends that helps. My husband stepped up and my mom was with us 3 days a week for the first few years, so that helped a lot.
Be prepared they may come early. 3 weeks on ave. but sometimes 1-2 months early. Mine were 3 months early, but with today's hospitals / equipment / knowledge / doctors / nurses they will help you til they're ready to come home.
Secondly was what to buy? Do I buy 2 of everything ??? 2 cribs, 2 swings, 2 everything? You can get by with 1 crib at first, they can co-sleep. They're so small at first and they probably like to be together.... at first. You'll know when it's time to get 2nd crib, for us 7-8 mos. old. Buy 1 swing/chair, if you want a 2nd later on...there's time. They don't need a ton of clothes, onsies and soft blankets are good enough. They'll grow out of clothes before you can buy more. My favorites were many hand-me-downs usually from friends, family members given to us. Cute, free, and then I passed them on if they were still in good condition.
You'll want a double stroller-either side by side or tandem. Tandem , the car seats slipped right in, heavier, but easier for narrow walkways, like store aisles. But the side by side was lighter, but wider. Maybe start with tandem with car seats and maybe the lighter side by side when they can sit up on their own...8-18 months.
I recommend diapers.com for diapers delivered to your doorstep. Good prices, variety, and convenient. Save yourself trips to the store.
You'll have more Dr. appts. Less sleep. Gets easier as they get older. The first few years are hardest. But it gets easier after age 4-6 somewhere.
Enjoy them every day. They Grow UP FAST!! Be prepared for this question every day... "Are they fraternal or identical?" But I don't mind...they're too cute!
The rest you'll figure out as you go along. Every set of twins are different from the rest. Some are easy...some are more difficult, but you'll find your family stride. Good Luck, have fun, Enjoy!!