After a few years of marriage, it's common to find the flame of passion slowly fading, but it doesn't have to be this way, says clinical psychologist Dr Harriet Lerner who has recently come up with 100 clever ways to get you and your partner to appreciate each other more.

In a book called Marriage Rules: A Manual For The Married And Coupled Up, Lerner points out that a successful relationship takes effort. "The fastest way to end a marriage is to wait for the other person to change," she warns.

Make the first move

Her belief is that it only takes effort on behalf of one person in the relationship for there to be a shift but sometimes this is the hardest part. "It's just when your partner is being the biggest jerk that you have to bring your best self into the relationship," Lerner explains on a YouTube video.

"When people come to see me with marital problems or with couple problems, they're always secretly hoping that I'm going to fix their partner. That's very normal - that we always focus on what the other person isn't doing for us or is doing to us."

But while our partners may need to change, it's important that we begin to take responsibility for our own behaviour in the relationship. It's not always about being right, but rather about doing what you need to do in order to get it back to a state that you're happy with. That might mean accepting the olive branch, burying the hatchet and turning your focus to better, kinder behaviour.

Be more polite

Lerner suggests making an effort to be polite towards your partner. At times, some of us can be nicer to complete strangers than we tend to be with our own partner. Pretending there is a guest staying in your spare room can help you to be mindful of how you talk to your partner.

Lerner explains that a high profile couple that she once counseled was constantly at each other's throats - until a respected colleague of theirs came to stay with them for a few months. Because he was in the next door room and could possibly overhear their bickering, they were mindful of how they spoke to one another. They told Lerner that never had their marriage been better than it was with their esteemed guest staying with them.

Don't nag so much

As you become more familiar with each other, the effort to make your partner feel good tends to be replaced by criticism. Lerner's rule? Bite your tongue and if you must, allow yourself just one criticism a day. As Daily Mail writer Kerry Hiatt observed, the restriction will have you feeling like less of a nag and if you hold out long enough, you'll let those silly, not-so-important criticisms go, whilst having time to think about how best to approach those that bother you most.

As Lerner explains, her book is one that's intended to offer straightforward ways to improve your marriage. "If you're the one with the courage and motivation and goodwill to follow even five rules, you're going to have a different marriage."