My husband and I have been together almost 15 years, married almost 8. We are soulmates and best friends. I actually think we've been together so long we've become co-dependent on one another!
Spend time together, but also have interests outside of each other. I have crafts and bellydancing; he's in a pool league. Togetherness is awesome; being in each other's company should be one of the best things. But it's also nice to be away from each other. Separate interests mean you have something new to bring to the table, something new to add to the conversation.
Oh, and separate checking accounts. We both have one, and a mutual one for bills. No one gets upset at who's spending the money; once the bills are paid, our money is our money.