In the Legacy Project, we interviewed the oldest Americans about their advice for living (which led to 30 Lessons for Living: Tried and True Advice from the Wisest Americans). We’re now asking hundreds of people married for 40, h50, 60 and more years about “trade secrets” for love and marriage. Here are ten tips to consider this Valentine’s Day.

1. Choose carefully. Marriage is perhaps the biggest decision any of us make. The elder view: many people are simply not careful enough. Don’t fall or drift into marriage without waiting until you know one another and you understand your reasons for getting married. Avoid making a commitment based on passion, panic at being left single, or inertia.

2. Keep an eye out for anger. The elders had trouble saying exactly what you should look for in a possible mate, but they are crystal clear on what to avoid: Someone with bursts of unreasonable and disproportionate anger, even if it’s not directed toward you. Many elders whose relationships failed say that they ignored a partner’s uncontrollable anger toward others, only to find it directed toward them later on.

3. Friendship is as important as romantic love. Most of the elders recommend that you marry someone who is also your good friend, who you enjoy being with. As one elder put it: “Your mate should be that kid you would have most wanted to play with on the playground in grade school!”

4. Don’t keep score. Marriage is a give and take proposition and sometimes circumstances will call for one partner to give more than the other. Happy couples don’t expect the give and take to balance out every day (or month, or year), but understand that at times you may be giving 90% and receiving 10% back, and other times your partner is in that role.

5. Talk to each other. Communication is absolutely the key to keeping a marriage on the right track. The elders say that the “strong silent type” may be attractive and mysterious, but if he or she stays clammed up about important issues, the relationship is probably doomed.

6. Be polite. In long marriages, people have learned the value of simple civility. They point out that we often talk to our spouses in ways we’d never talk to friends or co-workers: dismissively, insultingly, or disrespectfully. Simple politeness in spousal interaction, they say, can prevent many a spat or tiff.

7. Don’t just commit to your partner, commit to marriage itself. The elders confirm that all marriages go through tough times, but they stayed together through them because they took a vow and they respected the institution of marriage. This commitment forced them to work things out and come out better on the other side.

8. Find a partner who is a lot like you. Although we often say that opposites attract, over time fundamental differences can wear on a marriage. The elders say that you can have differences in backgrounds, but truly necessary are shared values. Check early on if your values on core issues (think money, sex, kids, religion, and work) are closely aligned.

9. They won’t change (much). What about taking a leap of faith and assuming you can change your partner after you are married? Many people do just that, and the elders basically think those people are idiots. Elder wisdom says that getting into a marriage with the goal of changing one’s partner is a fool’s errand, one that will doom the relationship before it really gets started. So if she’s always late or if he drinks a little too much, be sure you can accept it for a lifetime.

10. Don’t go to bed angry. It may be the biggest cliché around, but long-married people swear by it. Arguments should not be carried into the intimate space of the bed, and they are much more hurtful if they roll over to another day. Wrap it up, agree to disagree, or decide on another time to fight again. And even if anger is still there, they suggest you make some caring gesture before going to sleep that conveys: “I may not like you much right now, but I still love you.”