Living a life well-lived vs feeling like you've lived a life well-lived are two different things. The first... be a good person, treat others and yourself with kindness, try to leave the world a little better than it would have been without you.

Feeling like you've lived a life well-lived though, that's different for everyone. In the Sims games there are Lifetime Wishes. One wish to accomplish over that Sim's entire life. I think real life is similar - everyone has a lifetime wish that once accomplished will fill a hole and help them be more at peace with dying. I got lucky, mine was easy. I wanted to help someone in a way that positively impacted the rest of their life. When I discovered that I had accidentally done that for a friend, the effect was amazing. I felt spiritually whole and like I was done doing what I was put on this earth for. I'm not religious, btw. I'm still living so I'm going to keep doing my best... but now I feel like my life has been well lived.

I don't think the answer is so clear for everyone. My spouse doesn't know their "lifetime wish". Maybe it'll be revealed with time or maybe they'll never consciously know. I don't think it's something you get to choose, either. If you ask yourself what's the one thing you absolutely need to do to be at peace before you die then you may figure it out eventually.