Simple, but Happy Marriage Advice

I've talked to a few married couples that I really respect about what advice they have for a happy and successful marriage. One of my best friends said that she has grown in so many ways, especially in matters of communication. She told me this, "You realize that communication is essential. If you don't say how you feel then the other person won't know.. My husband can't read my mind apparently! But with that you have to say things in a way that they come across the right way too.  So that's a way we have both grown, we are learning how to better communicate. And  something we do to have an effective marriage is really just simple things like telling each other that we love and appreciate each other. The little reminders really do mean the world and are a reassurance every day that it was the right decision. Even if we start to disagree or get frustrated with each other if we just say "I love you" then we both can calm down and take a chance to effectively talk about things and resolve the conflict quickly. But also you grow a lot because you're almost forced to think about someone else's life. Like it's not just you it's both and it's important to take care of both of you. No selfishness anymore!" 
I went on a walk with another best friend and she told me that one of the things that is really important in their marriage is that they support each other in what they love to do. If her husband has a basketball game, she goes to watch him. They cook together and constantly do things that make the other happy. She told me that it means the most to her that her husband cleans the house every day before he goes to classes so that when she comes home from work she can get other things done. They make sure that they value each others love language by demonstrating their love and appreciation for each other. 
I once asked my mom how she and my dad avoid arguments. I have never seen them argue, and am also old enough to know that they don't just have them behind closed doors. They never fight because of this simple piece of advice that my grandma gave them when they got married- she said, "Remember that you love each other more than you love being right." 
When I have talked to different people about advice for a successful marriage, one person suggested to never stop flirting or attempting to "woo" each other. Just because you are married doesn't mean that the effort ends after the ceremony. Constantly date and complement each other. 
Another piece of advice I received was to always consider the other when making decisions. Decisions no longer revolve around you, they have everything to do with your spouse as well. 
I know that one of the reasons that I respect these people so much is because of all of their wisdom regarding marriage and selflessness. I know that no marriages are perfect, but two people striving towards perfection together sounds happy to me.