Did you know that Friday was National Best Friends Day? Neither did I until the day was nearly over. But it doesn't really matter--your friendships are something you should think about and nurture throughout the year. It turns out that having close friendships is surprisingly good for your happiness and health. One study even showed that friendships are a better predictor of longevity even that spousal relationships.

In fact, researchers at Harvard have found that not having close friends is as bad for your health as smoking, according to a blog post by Wendy Capland, executive coach and bestselling author of Your Next Bold Move. Capland is my coach, and for the past couple of years, she's been coaching me and I've been writing about it

Close friendships are good for you in every way. Even if you're happily married, you probably know that spending time with close friends is an important way to get perspective on your relationship and widen your horizons beyond your primary relationship. But what if you feel like you're just not good at friendship? What if you aren't sure how to nurture these all-important relationships? 

Here's Capand's advice: 

1. Don't be afraid to be the one who maintains the relationship.

Have you ever had a friendship peter out because you got sick of always being the one to call or text or suggest getting together? I know I have. Capland says you shouldn't get hung up on this issue--in fact she says she takes the initiative most of the time in her own friendships. "I actively, regularly, and consciously nurture my friendships that are most important," she says. "I'm usually the one who sends the text saying 'I haven't seen you for a while. Let's do something about that.'" 

Relationships and connections are among her top values in life, she says, and she makes sure to live that value. "I don't wait for someone else to make the first move."

2. Don't separate your personal and professional lives. 

Like me, and probably you too, Capland is very wrapped up in her work and career. So one way she makes her friendships count is by bringing her friends into her professional life. Capland's popular women's leadership retreats and workshops started out as an evening where she invited her 10 closest friends over to discuss their careers and work lives. 

"I said, 'I'm thinking about what I'm going to do next. I feel a little unsettled about it and I'd like to have an evening where we talk about it. Would you be willing to come?'" she recalls. Over time, that group became what she calls her "board of girlfriends." "They guided me and helped me shape and define this work in the early days," she says now. If it wasn't for this group of women, I wouldn't be doing these programs today." 

3. Find friends who will support you and help you be heard.

We all need support. But, as Capland notes, women in particular may need help getting our voices heard, especially in meetings and other group situations where, as research shows, men seem to instinctively dominate conversation. By working together, women can mitigate this tendency and amplify each other's voices, as a group of women in the Barack Obama White House learned to do. Having friends can make the difference between having your ideas hear and being ignored. They should also be able and willing to provide what Capland calls "extreme support" which could include anything from taking care of you when you're ill to being willing to help you, sponsor you, and share their contacts with you to help your career. "Extreme support is necessary; it's not optional," she says.

4. Be choosy about your friends.

The late Jim Rohn, the legendary motivational speaker who gave Tony Robbins his start, said that "You are the average of the five people you spend the most time with." And research actually shows that if you spend time with a friend who gains weight, you are likely to as well. So be choosy about your close friendships--select friends whose attitudes and behavior inspire you to be your best self rather than enabling you to be your worst.

Capland says she selected her original board of girlfriends because they were women "who could best help me sort through what I wanted and what I was passionate about." These days, she says, she also looks for friends whose successes inspire her in her own work. We've all had the experience where becoming friends with someone who's achieved something seemingly impossible suddenly makes it seem doable. So use your choice of friends to inspire you to greater heights. 

5. When it's over, be ready to let go.

Capland advises seeking friends at the same stage in their lives and careers as you are. It can be tough to be close with someone who's fixated on retirement when you're still climbing the ladder, or someone who's entirely wrapped up in their new baby when you're single and focused on your career.

At the same time, it's important to recognize when a friendship has run its course and that it's time to move on. "I think there are friends for certain times in the life cycle and when those times are over, those friendships are done," she says. There are only a few friends who will really remain in your life for the long term, and they should be the ones who truly support and inspire you, she explains. "You have to be careful about the people you bring into your inner circle."