1. Work out your pressure points
Once the novelty of living together has worn off (and it will) there are going to be things about your partner that drive you crazy. If your boyfriend leaving the toilet seat up turns you purple with rage you're going to have to talk to him about it and he's going to have to remember to put it down. Because one day you will probably rip the seat off and throw it at him. Similarly, if he can't stand the way you leave teabags in the sink you're going to have to work on that. Be as mindful and considerate as you, a flawed human being, can be, and remember to give each other some leeway too.
2. Figure out your finances
Are you going to have a kitty, take turns getting the groceries, have a joint bank account, or a spreadsheet that details every dollar spent? Work out a finance situation that is fair, effective and manageable. This avoids resentment and awkwardness, both of which are total mood killers.
3. Get the cleaning roster sorted
Depressing research shows that women still do more housework than men, and frankly that's not good enough. Divvy up the chores evenly, and choose the one most hated chore that you each refuse to do. Or get a cleaner. And none of this "make it fun" business. Housework isn't fun, it's called "chores" for a reason.
5. Make it official
As in, put both of your names on the lease and all the bills. Common sense isn't the death of romance.
6. Make sure you each have a room/nook/shelf of your own
This isn't just about divvying up the storage space evenly, but acknowledging that at times you're going to want to do your own thing – whether that's reading a book in the sunny corner of the living room or building model trains in the basement. Doing things just for you is key to a happy relationship, and no matter how weird or embarrassing you think the other's hobby is, allow it.
7. Be willing to compromise
Maybe this is the biggest thing about living with somebody else, whoever they are. You've got to be willing to not get your own way all the time, and to forgive other people their oddities and bad habits. We are, after all, only human.
8. Don't cheat
By this I mean watching episodes of the TV show you're binge-watching together when they're not home. This is unforgivable.