We got married at 23 with no kids and had never lived together. We've been married almost 5 years now and have 2 kids.
I enjoyed being a young wife. I was sick of dating and vowed not to again until I was engaged. He felt the same way, so we went into marriage knowing exactly what we wanted. There was no pressure and no pretense. There was a steep learning curve, though.
I think we were both still fairly immature. We were mature in other ways, like we had both been out on our own, working, going to school, paying bills, etc. But I was still spoiled and he wasn't used to taking care of someone else, so we had a few disasters.
I don't think living together first would have changed anything, though. I think marriage is a spiritual thing, so no matter how long you live together, there are going to be some things you just aren't privy to until you say "I do".
Kids have definitely changed us, but for the better. We are more giving and focused. We are bonded in a different way now.
Do I always look cute at home? No.
I don't look nasty or anything, but I definitely could look better. I can't even lie and say I'm working on it.
I'm kind of scared to see what would happen if I did look cute around the house. I don't think he'd leave me alone.
The only tips I can think of are to go in with the knowledge that feelings will change sometimes, but making a marriage work is about making a concious effort to love your spouse. I also like what MissScarlett said about people changing. I think early 20's is still a time of discovery, so you may in fact become a different person when you hit 30. That's ok, you just have to be prepared for it. I'm finding out some good stuff about myself now that is totally different than how I felt 5 years ago.
Congratulations to, umm, anyone for whom that's appropriate.