In my humble experience of three years of being married, I have come to believe that there are few key ingredients to a happy married life :

• Friendship - you should be friends first & spouses later. You don't need to be friends for years but you do need to have that bond, just like friends, where you understand each other in a very meaningful way, where you know the other person’s strengths & shortcomings, & have candid no-bars conversations, just like a friends do.
• Understanding & Maturity - I cannot emphasise this enough. Understanding each other & being mature about each others’ needs is critical. No matter how well you connect, when two different individuals come together, there will always be some friction. Understanding is the lubricant that helps ease these friction points.
• Adaptability - This is actually a part of understanding. You need to adapt to your life partner’s needs. They may have a different point of view towards things than you do. And if it is not a mission-critical topic, try & adapt to each other’s needs. It will make life very smooth & happy.
• Intelligent Conversations - This is a natural outcome of understanding & adaptability. There are always some things that you cannot adapt to & you need to have intelligent & mature conversations about those. Without taking the topic to your ego, you need to put the relationship above both of you & just talk it out. Agree to Disagree. You are two different individuals & its okay to have differing views.
• Love & Physical Intimacy - & of all the talks above, romance & physical intimacy is one of the things that make your relationship as spouses unique, that you can (& should) have only with one another. It does help create a special bond.
• Unwavering Support - Each one of us goes through a difficult phase in life. That is when a healthy relationship with your spouse matters the most. That is when you are the most fragile in your life & that is when you need your partner’s support the most. Make sure you are there for each other at their lowest point, when they need you the most.
• Honesty - No relationship, not even friendship survives without honesty. This is most important relationship you will ever have in your life. Be honest & faithful to your partner. That develops an implicit trust that helps navigate the highs & lows of life.

Those were my 2 cents.

Hope that helps! Have a beautiful life!