There’s another thread about rekindling marriage, which got me to thinking about taking a more preventative approach. For the couple who are already doing well, but who want to take it to another level and go deeper, what techniques do you recommend? Not just sexually, but in all respects. Me and mine have been writing long letters to each other, and it is working wonderfully in terms of opening up to each other and getting to know each other better. But we’d like to know what other things we can try, especially face to face.
Backpack together, or do something else that’s difficult and physically demanding and lasts a few weeks. Build something together, something serious and difficult, like a water wheel to supply power to the house or something.
Doing something difficult that is new to you opens up a whole new side, IME. There will probably be some fighting, but you learn to get through it and you learn more about each other. And at the end you’re left with great memories and the feeling you have accomplished something together. 
My parents belonged to a couples’ growth group, there were some tasks they were supposed to do in order to improve their relationship.
Some which I think can be relevant:
- Set up things to talk about which are not “family and work”: do things such as both read the same book and later comment on it.
- Have a sit-down talk at least once a month.
- Set up personal goals which are geared towards improving the relationship. They can be complementary (“take out the trash without being told to”, “set up a time before which I will not remind my partner to take out the trash”) but do not have to be. They should also be verifiable and appropriate in size (“be better at money” isn’t really verifiable, nor is it dimensioned; “clear the closet in the hallway and toss away at least half of its contents” is verifiable - it will be size-appropriate depending on the person involved and on what’s really in that closet).
Purchase a large piece of IKEA furniture, some assembly required.
Spend some time each week doing something she particularly wants to do (even if you don’t), and vice versa.
Go to bed at the same time and engage in “pillow talk” before you fall asleep. Because it’s dark and you’re sleepy, you share a lot more stuff than any other time of day. It works for me!
Develop or pursue mutual interests, communicate well, trust and be trustworthy, be honest and open, be quick to forgive and slow to anger.
Is it foolish to say spend time together? I get mocked sometimes because I do almost everything with my SO! I’ve even been called co-dependent. I prefer to call it interdependent. I love him, why wouldn’t I want to spend time with him? He’s my favorite companion in most things.
So spend time together. Lots of time.
And good psychological advice from that book. Never let the sun go down on your anger. Anger stored is anger that grows.
And never, ever hang wallpaper together. Or else.
Do something you’ve neither done before, or go somewhere you’ve neither been before. I’m pretty sure this is what the honeymoon was really for. Suddenly it’s the two of you against the world, whether it’s deciphering a map in a foreign city or the room service menu, you will/should instinctively/intuitively “pull together”.
It only requires a new experience where no one is ‘the expert/has experience’. You will have to rely on each others contributions, each others strengths and patience. The more challenging the experience, the better, but not to the point where anyone is truly out of their depth.
You build a history of working together, whether to put up the tent in the rain, or explain to a foreign language taxi your intentions with mangled language. It is almost unavoidable that you will share a success, a memory, a reflection, something to look back on and laugh.
Come whatever may, any dark time really, you’ll always have those moments to look back on. When you were working together, when you succeeded.
It seems to me, you can never lose this gem, it can never be taken from you, or be undone.
You think that’s bad? You ever removed wallpaper?
Or used a boat ramp. I swear every time my dad used to drag us fishing my parents would almost get a divorce at the boat ramp.
I’m the poster that started that other thread, so take this advice with caution 
But I think travel is great for a couple. IF they do it well together. You find yourself in a new environment with really only each other to count on. It forms some serious bonds. That, and you have lots of stuff to share afterwards. Stuff that the two of you have experienced together.
Have adventures together. We have a long weekend coming up and I texted my wife (of 21 years) yesterday and told her that I want to explore this weekend. Go someplace close by that we have never been, or haven’t been for a long while. It helps that we don’t have kids but I still feel like I’ve never really stopped dating my wife.
Doing big projects around the house is also good, building furniture, painting a room, etc. Just spend time doing something out of the ordinary. All you need is the will to do it.
This is also so true. It’s been 12 years and we still always go to bed together and have pillow talk. If one of us stays up late to finish a paper or something we miss each other!
It means we finish off each day together, just the two of us. 
That one will depend on the couple; I think it’s a great idea when it works well. My mother hated it that it was when Dad would “spring on her” stuff he’d been thinking about and she hadn’t (he was the one most likely to think ahead, he’d start looking at the vacation budget in January, she still thinks hotel nights* grow on trees); she’d be taken off-guard and start thinking about whatever it was, but by the time she was able to come up with a half-coherent answer or question he’d be dead to the world.
- and train tickets, and theatre tickets… no, Mom, if you want to go to the theater today at 9pm, telling me today at 8pm is way too late. You may be able to buy a ticket at the theater’s own window, but that means bringing your butt there.