First rule of relationships: Trust.

Trust.
This is the easiest to lose and the hardest to gain back. Without trust, there would be no foundation in the relationship, there would be no core with which it could hold on to. You must learn to trust yourself before you can begin to trust others.

Have faith in your partner.
It comes right after trust. Faith is that blind belief that everything has its purpose, that everything will work itself out in the end. Faith that your partner loves you as much as you love them.It is believing no matter what.

Open the lines of communication.
Don't just let the gray areas be gray forever. Without communication there would be no understanding. It's hard to read between the lines all the time, sometimes talking it out strengthens the already existing bond between you two. By airing out whatever is bothering you, and talking it over, you come closer to a comfortable solution.

Be thoughtful.
Let your partner know that he/she is constantly on your mind. Giving something as simple as a text message can guarantee a sense of warmth and love. Don't be lazy. Take time and give effort to make your partner happy.

Never take your partner for granted.
This is a complete no-no. Just because you've been together for several years doesn't mean that you can't be sweet anymore or that you won't go out of your way to do something for your partner. Always appreciate, no matter how insignificant and how small...be appreciative.

Love yourself.
See your self-worth. You cannot fully love someone else if you haven't accepted and love who you are.