I think that if you'd asked me how to make the world a better place I probably would have had a different answer every decade, and who knows? Perhaps my answer will change again; but for now, my answer is this: Joyously and consistently take ikigai-congruent action, constantly raise your standards, and celebrate along the way.
There are some standbys that seem to be universal: Get a good night's sleep, exercise and meditate every day, drink plenty of water, keep your goals in front of you, and do your best to get all six infinity stones, but I think that top paragraph is really the key.
If you have your life purpose, and you are moving towards it, you're on your way to changing the world, because a life purpose by definition serves others and thus, changes the world.
I think all too often we look for an instantaneous way to solve all the world's problems. And hey, if you happen to be one of the richest men on the planet and you want to tackle malaria, cool beans man, have at it. But for the majority of the population, I think a life purpose should consist of a way of being.
I *do* believe in epic visions, grand plans and massive action. I do believe in obsessive skill acquisition to achieve those goals, because progress equals happiness, and a killer ikigai is a surefire way to want to make and measure that progress.
But I also believe in a daily mission. Compound interest goodness. Being good every day along the way to change the world for the better with every minute of your life.
I think that's ultimately the key to happiness. It's great to rid the world of malaria, but it's arguably better from a personal perspective to be an amazing dad while doing that. It's arguably better to enjoy your morning, be nice to the grocery clerk, say hi to your mail delivery person and also do an inordinate amount of research on mosquito-zapping lasers.
That's why Tony Robbins is always saying live with passion. It isn't "have an all-consuming passion that deteriorates your life" it's LIVE with passion. Your ikigai, your purpose, your techne, your driving goal should enhance your life and give the awesomeness that is you meaning.
It should define why you are here, but not to the detriment of actually being here.