#1 - Hydrate
When pregnant with twins, you need more water than with a singleton (which is more than you need when not pregnant). My goal each day was 12-15 glasses of water.
Ways to Stay Hydrated:
Drink a tall glass of water right when you wake up
Drink a tall glass of water with each meal and snack
Keep a 16-24 oz bottle of water with you at all times and drink
#2 - Rest
All expecting moms need lots of rest, but when you are carrying multiples, you need even more. My goal each day was to really listen to my body and rest as needed. I always rested during my son's naptime (roughly 3 hours), after dinner until bedtime, and during the day as I felt I needed it. At the end, I pretty much rested all day. If you are tired, take a nap or go to bed earlier as you don't sleep as good at night (especially at the end). Let others help you with housework and errands.
#3 - Take Your Prenatals and Any Other Supplements Your Doctor Recommends
I took my prenatal vitamin everyday and I know it helped the babies and me to get those missing nutrients. When I got further along, my doctor had me on Vitamin D to prevent pre-term labor. I never missed a dose. Figure out a consistent time to take them and buy an extra bottle (or make a baggie) to keep in your purse so you never miss them.
#4 - Register Early
As soon as you find out the genders, go start your registry (some people even do it earlier but I didn't want to have to do it twice). I started mine in the store and did a lot online when I got home. It was exhausting even at 18 weeks, so don't put it off. Have an organized list (I put mine on here) and that will make it a lot faster. The more work you do ahead of time, the less running around the store.
#5 - Get the Nursery Ready Early
Again, as soon as you find out the genders, get going on the nursery. If you have the basics (crib, furniture) setup and the room painted/decorated, it will make it easier when you have your showers and have a lot of stuff to prepare. My goal was to have it done before the 3rd trimester.
#6 - Have Your Shower(s) Early
I highly, highly recommend having your shower(s) early. You get what you need and have enough energy to put it away, wash baby stuff, etc. You won't be as big and uncomfortable so you can enjoy it. And, you (hopefully) won't be on bedrest so you can attend. Again, my goal was to have my showers before the 3rd trimester.
#7 - Pack Your Hospital Bags Early
I didn't do mine until 34 weeks (4 weeks before my scheduled c-section) and it was fine, but I would recommend doing it as early as possible. If you don't actually pack the bag, get all the stuff you will need and have it laid out (pack if possible) and have a list of what to pack (personal care items) next to it so you can pack quickly.
#8 - Never Hesitate to Call Your Doctor
There are a lot more things that can go wrong or happen earlier with a twin pregnancy. If you have any concerns, call your doctor. Some people don't and they are in pre-term labor. It's better to go and be perfectly fine, then to not and have a problem.
#9 - Follow Doctor's Orders
Again, there are a lot more things to watch for and be careful of when pregnant with twins. Do whatever your doctor says (whether it be take a specific medicine, rest, pelvic rest, drink more water). They know what they are talking about.
#10 - Be Prepared for 1 Million Questions/Comments
When you are pregnant with twins, you will get a ton of questions/comments, some friendly, some annoying, and some down right rude. Just know you will be getting them, figure out some simple responses, and pray that you can be nice no matter what. I've had to bite my tongue a lot (more with comments than questions). From what I've heard, it just gets worse when the twins are actually born and you take them out in public.
#11 - Stock Up on Diapers, Wipes, and Any Other Baby Needs You Can
I had 2 diapers/wipes showers and got a ton of diapers and wipes (and other baby bottom needs). I also started couponing and watching for good deals on them about half way through. My goal is to get diapers for 10 cents each. We set up a shelf in a closet and just collected all sizes. My hope is that we won't have to get them too much and when we do, we always get them on sale and use coupons. My favorite places to get diaper deals are CVS and Rite Aid.