get some sleep, have some sex, because it will not happen that much afterwords. seriously, if there are things that you want to do with your wife, just the two of you, do them, now, right now.
there is a good chance the twins will come early, be ready for that. they may be smaller than other kids, be ready for that, too.
not to be paranoid, but have a birth plan, and make sure that it is communicated with the medical staff - how your wife wants to be medicated, anything special you want with the babies (will you cut the cord, etc?). what we did, right after the babies were born (well, a few minutes), my mother in law came in to be with the wife, and I stayed with the babies, where ever they went. sure, it a hospital, but I prefer to keep an eye on my kids, just in case. then, when they brought the babies back, I came back. but I stuck to them as long as they were away.
if you are taking pictures, have everything ready, but you are secondary to the process, so don't get in anybodies way. take a lot of pictures, but don't post anything until your wife vets them.
wear comfortable clothes with lots of pockets - you may be in them for a while, and the rooms can go from hot to cold quickly.
make sure that the doctors, and espectially the anesthesiologist, understand that you are rational, serous people. you want them to communicate with you when needed, but don't need them to fill you in with all the stupid details.
get the twins on the same sleep schedule as quickly as possibe. this is easier said than done, but my wife did it very quickly (maybe 6 weeks) and it was very helpful.
some women can't breast feed, some take time to get the milk flowing. your job is to shut up and be understanding. it is great if they can do it, very healthy, and frankly it won't do as much damage to your wife's breasts as you may think. but keep in mind that is she can't, it isn't the end of the world and you have to let her know that.
your wife will be nuts, totally freaking nuts, right before, during and after giving birth, maybe for a month or so after. suck it up. she will have huge amounts of hormones running through her.
if you can, take a course on birth - but what you must do is watch a movie so that you know what to expect.
one twin may be bigger. you may like one twin more, sometimes, and sometimes you may like the other one more. one may pick on the other. all part of twins.
your job is not to be their friend, it is to give them tools to be healthy, successful adults.