(CNN) With the holidays in full swing, you and your partner are probably more focused on family, travel and food than on spicing up your sex life.

"We'll do it more in the new year," you may resolve. But pretty soon, looming work deadlines, your kids' busy schedules, and even just the lure of your sofa and the remote control conspire to keep sex on the back burner.

And that's a problem. Sex is the glue that holds us together, and without it, couples can begin to feel like roommates or "just friends" at best. In my experience, when couples stop having sex, their relationships become vulnerable to a host of other threats, including anger, emotional detachment, infidelity and even divorce.

The great thing about ruts, though, is that you can climb your way out of them. "Research shows that couples who communicate well with each other are better able to navigate sex ruts so their happiness and satisfaction aren't seriously affected," said sex researcher Kristen Mark.

In fact, there's good evidence that, when it comes to sex in long-term relationships, quality typically trumps quantity. In three recent studies, researcher Amy Muise and her colleagues at the University of Toronto Mississauga sought to determine whether the amount of sex couples had was related to their life satisfaction.

They found that for people in relationships, sexual frequency was associated with greater happiness, but that this link stopped being significant at a frequency of more than once a week. That suggests that you don't need to have sex every day to feel connected to your partner but that you should go for it once a week!

Is sex on your schedule?

So what's the solution for busy couples? Like anything else you schedule with your partner, I believe you should put sex on the calendar. Many people will wrinkle their brows at this: "While it's OK to plan everything else in our lives, sex should be spontaneous, right?"

Not necessarily. Desire drives sex, but there's not just one type of desire. "We can imagine spontaneous desire as a lightning bolt to the genitals -- kaboom!" said sex educator Emily Nagoski. Media representations of "hot sex" almost always depict this type of have-to-have-you-now encounter, which is most common among new couples.

But desire isn't always spontaneous. It can also be responsive, emerging in response to something that came before it. What's that something? Arousal.

In the Upanishads -- one of the oldest Hindu texts -- we are told that the energy that supports all creation manifests as the warmth that arises when we are touched. To me, that is arousal: the pleasure of your partner touching you, for example. So if you're waiting for spontaneous desire as a reason to have sex, it may never happen. But if you allow yourself to feel some sort of arousal, desire has much greater chance of emerging.

"Responsive desire is normal and quite common in long-term relationships," explained Mark. "Sometimes, we misconstrue that as low desire, but it isn't. Desire is a state, not a trait, and it ebbs and flows for everyone. It's just more difficult to be spontaneous in established relationships -- that's why it's important to make sex a priority."

Rev your engine

If the very thought of sex after an exhausting day has you dragging your feet, it helps to focus less on desire and more on generating arousal. We can do so by understanding what's called the dual-control model of arousal.

Think of your sexual brain as a car. The first part of the model, the sexual excitation system (SES) is like the gas pedal for your sexuality. A lot of things can press that pedal and rev your engine, from visual stimulation (how you feel about your body, how you feel about your partner, even having a good day at work) to tactile stimulation (having your partner touch you). Your SES constantly scans your environment for "excitors" that may be sexually appealing and then sends signals to your brain and genitals to activate them.

The second part of this model is the sexual inhibition system (SIS). Just as your SES acts like your body's gas pedal, your SIS puts the brakes on your sexuality. Like the SES, your SIS also constantly scans your environment but for turn-offs, whether that's an argument with your partner, an uncomfortable bed or even that pile of dirty dishes in the sink. We all have both an SES and SIS, and we all need both for a healthy sex life. That makes arousal a two-part process that requires providing stimulation for the SES and removing any that might trigger the SIS.

How do you do that? It helps to think about how to ease off the brakes and step on the gas. You and your partner might want to write down your excitors and inhibitors and share them with each other. Your partner loves the look of you in lingerie? Go shopping for some together. Can't get turned on until the house is clean? Make a plan to divide and conquer the mess.

A willingness window

So here's the real resolution I'd like you to think about for 2017. Rather than just trying to have more sex, I'd like to go back to that principle of having the willingness to generate the arousal that will lead to desire.

Resolve to create a "willingness window" once or twice a week for 15 minutes and decide with your partner on an arousal-generating activity you can put in that window.

In my experience, some couples miss kissing and making out, so they commit to 15 minutes of above-the waist connecting. Try massage, dancing or taking a tender shower together. One couple I worked with even wanted to wrestle.

Remember, the brain is the biggest sex organ and we can get turned on without any physical touch, so I also encourage couples to think of a mental activity they can put in their willingness window: Share a fantasy, read some erotica, watch a sexy R-rated movie or even watch some ethical porn together

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I don't think of planning sex as routine or boring but as mindful, caring and attentive to the value of sex. And if you're having problems mustering the desire, then just commit to the willingness window. The exercise can still be fun.

"A lot of the time what happens is that you just put yourself in bed, touch (your) partner because you put it on your calendar and said you would, and you remember that you like it," said Nagoski. "It can feel a little routine at first, like, 'time to make the doughnuts.' But doughnuts are delicious -- and so is good sex."