Good advice and sentiments here. Ours are 20 and 23 and have grown up to be great young adults. They will test you, surprise you, anger you, make you happy and everything in between. They'll scare you, make you proud, push your patience to the limit and give you joy like you've never had before. Yes, you need to be their rock but they also need to see that you're fallible. You need to instill good values and at the same time see that you're not perfect as they never will be either. They need to see you laugh and cry. They need to see you and your wife interact, support and love each other and above all, they need to KNOW you love them. Every day. My parents were not good examples but I learned a lot of good things from each of them along with other family members. I also swore not to make the same mistakes they did raising me. Yeah, right. My dad's poor attitude and mistakes came out of me now and then and you have to make sure you check those bad influences (if you had any) quickly. You're not their friend, you're their parent - never forget that. Be careful to discipline when necessary but don't break their spirit. You can be friends but the bottom line is, you're in charge and they need and desire that from you. They need to be encouraged to be independent and make their own choices, as well as be responsible for those choices, good or bad. Spend time with them - lots of it - make it your priority because every time you're not there, they will remember it. Trust me on that one, my dad was never at my ball games, school plays, any of that and it took years before I forgave him for that.
Most of all, congrats! Your life as you know it will be very different once that child is born, but it's worth every single second.