At first, it's sort of funny -- the dirty underwear on the floor on his side of the bed, her 10 bottles of product crammed on the bathroom shelf. "Cute," you both chuckle. "I'm in a relationship!"

Now, fast-forward a few years. Still laughing? Maybe not. According to Peter Post, the great-grandson to etiquette guru Emily Post and the author of Essential Manners for Couples and Essential Manners for Men, those thoughtless quirks are the little things that, like death by 1,000 cuts, strain a relationship.

"We get to the point where, instead of compromising, we're just not willing to do another thing," he says. "Unquestionably, we do create potholes that don't need to be there." Navigating those speed bumps requires a bit of consideration and etiquette. Here are the top rules for relationships.

1. Don't be demeaning
We all occasionally take each other for granted, but putting down your partner, ignoring them in favour of a smartphone or deliberately belittling their achievements is the kind of thing they'll remember for a long time, says Post.

2. Compromise
Rules are meant to be broken, so be willing to take each situation as it comes and adjust appropriately. "Successful couples end up resolving this type of thing by deferring to the partner to whom the issue matters more."

3. Don't play the blame game
Accepting your responsibility when things go awry isn't just smart, it's respectful, says Post. "Don't hold your choices over someone else's head if it doesn't work out."

4. Schedule a date night
Whether it's a movie and popcorn at home or a stroll to your favourite patio for a drink, couples should work "just as hard on their own relationship as they do in raising their children," he says.

5. Resolve in-law issues
You may not like your meddling mother-in-law, but you have to make an effort to find even a small patch of common ground. And no matter what, never disparage your partner's relatives.

6. Skip flirty fun with others
Flirting isn't a good idea, says Post. While it's mostly harmless, you should stay within acceptable limits and never say anything you'd be embarrassed to have your partner hear.

7. Remember the little things
If your partner makes your tea every morning, make sure you reciprocate with a small unlooked-for gesture. "It's amazing how that will impact people," says Post.

Photography, iStockphoto.com.