Hell if I know. I know what doesn't work...

It is possible to make no mistakes and still lose...

ok like @atheist your question caught me short. I am here in part because I haven't learned the answer to that question. Oh, I could sprout lots of sage sounding advice and then doubt your intelligence if you took any notice of me. Sorry.

If your partner is. a narcissitist , run away

Mutual support in each other's fulfilling their identity, each other's dreams and accomplishments, caring for each other's feelings leaving expression of this always open, being positive and non-competitive, not being critical, accepting each other's quirks, having a meeting of the minds, being affectionate, having each other's back, sharing goals, having lots of fun in bed, laughing a lot, of course, being honest with each other.....It matters that they should be equally intelligent and share interests.

I think a successful (by which I mean strong, happy, loving) is a lot of hard work. It can be very difficult adjusting your life to mesh with someone else's. It requires dedication, consideration, respect, and equality. Liking your partner as well as loving them is also important. So are compromise, open-mindedness, and a willingness to really listen and consider the other person's thoughts and feelings. Trust is essential. Above all, it means always remembering that your is the most important person in your life.

I was going to answer your question but then I realized that all of my romantic relationships have failed. So I'll pass.

If you are more specific, I'll try to answer.

Time, tolerance and talking things through with the occasional hug and pleasant surprise thrown in.

Trust & Magic

Never underestimate the raw power of the helicopter dick

Going to church and praising god.

Having a mutual sensitivity to the other persons ideas ideals, wants, needs ,I don't mean being a doormat, more just considerate of each others profile for living. My partner and I live in the same building but don't live together so if we get to a sticky place its a good time to make a good exit and each sleep on it and do apologies/post mortems later if they are still needed.Lovingkindness I think is a good ideal and to remember why you actually like each other. (But then thats just my recipe I am sure other couples have far more dynamism than we do)

I do not think that basic incompatibility can be overcome. Outside of that openness, affection and honesty, tempered with compassion.

Distance.

I think good old give and take and being forgiving enough to be kind & completely honest about what rubs you up the wrong way - Also never let the sun go down on an argument and remember the good parts of your friendship before getting picky with each other . If you can laugh about it all afterwards thats a good sign. I thnk its a good idea to have a talk about having no -go areas about things that perpetually lead you into that 'not talking just sulking space.

Me and her working for the same common interest.

I assume compromise, willingness to be understanding and to compromise, and a will to make it work.

Sex, drugs and rock n roll ! Same political agenda! Anyone seriously need further explanation see me after class! This and all I state or promote is open for one on one debate always.

Im single

Looking for some ideas?
I would suggest you give the idea of the "Emotional Bank Account" a try and, if you are prepare to accept the other person for who she/he is (not try to change them), this idea may take you a long way into a heathy relationship. BTW, this applies to all relationships that you care about, your spouse, your children, coworkers, etc.
In a nutshell: When it comes to improving and maintaining our relationships with others, Stephen Covey’s metaphor of the Emotional Bank Account is probably one of the most powerful ideas ever created for the development of interpersonal relationships. If you’ve never heard of this, it basically means that anyone with whom we have a relationship with, whether it be our coworkers, family or friends, we maintain a personal “emotional” bank account with them. This account begins on a neutral balance. And just as with any bank account, we can make deposits and withdrawals. However, instead of dealing with units of monetary value, we deal with emotional units.
The emotional units that Covey speaks of are centered around trust. When we make emotional deposits into someone’s bank account, their fondness, trust, and confidence in us grows. And as a result our relationship develops and grows. If we can keep a positive reserve in our relationships, by making regular deposits, there will be greater tolerance for our mistakes and we’ll enjoy open communication with that person. On the contrary, when we make withdrawals and our balance becomes low or even overdrawn, bitterness, mistrust and discord develops. If we are to salvage the relationship, we must make a conscious effort to make regular deposits.

The answer to the question "What makes a relationship work": if it's a relationship that is important to you, constantly make deposits to maintain a positive emotional bank account that is balanced with the other person's bank account.

More details [lifetrainingonline.com]

There was a study in Sweden (or Amsterdam) that men were recruited to accept any opinion or decision of their wives for 6 months. Things went well for a few weeks--until the women were getting angry and physically abusive towards the husbands. The best advice for relationships is to be flexible...but don't take any shit.

As others have mentioned, trust, honesty, reliability, appreciation, respect. You have to have each other's backs. And as you get to know them, you realize you want to know so much more.

I kind of hate to be that guy, guy. But I don't believe there's any one-size-fits-all answer to that question. What one person is looking for in a good relationship can be completely different than one another person is. There is some overarching criteria in my opinion but nothing that really applies the same way to everybody.

Trust
Dependability (knowing that you can rely on them)
Mutual devotion

When I was younger I probably would have put in something about mutual interest and being attracted to the other person, as I get to know more people and see more more relationships that are "unconventional" I see that a great deal of relationships are "unconventional" in some way and still work for those a part of them.

Then again if we had love and the desires of the heart really pinned down all poets would be starving, not just the bad ones

If I had any idea I wouldn't be single

Doing just the opposite of what I have been doing apparently.