Most people pursue happiness in life but they can never achieve it unless they are happy in their relationships. Relationships form the foundation of a person's emotional state and his happiness or grief more of less depend on the way he is emotionally. You see in order to make sure there are no bumps in a relationship you must follow some extremely essential principles.

Be flexible - Relationships are all about making compromises therefore learn to be flexible instead of rigid. You should be willing to shed your ego whenever necessary and consider the wants and needs of your partner. You see it's more or less a two way thing and a relationship can never survive in the long term is one of the partner is unhappy with the other.

Admit to your mistakes - One of the best possible ways to end all arguments within a matter of seconds is to simply admit to your mistakes instead of fighting over them. You see admitting to your mistakes does not make you small rather it gives your partner the indication that you are strong enough to admit to your mistakes whenever you are wrong.

Make your partner feel wanted and loved - Now this is the core foundation of a strong relationship. Every human being has a basic need to feel significant and feel loved. And this love has to be unconditional. You see the moment you start taking your partner for granted the relationship starts going down hill. This is the major reason why you must make your partner feel loved and wanted.

I think respect, stability and common interest can make or break any relationship. Keep that mind next time you go out on a date, meet a new friend at a party or start a new job.

I'd like to add communication, respect, honesty and mutual understanding.

I second communication, respect and honesty. To me, a relationship isn't about the good times and making your partner feel loved because frankly, anyone can achieve that; it's really about how you deal with the bad times that makes you stand out from every person she/he has ever been with.