If you had a chance for a ?do-over in life, what would you do differently?

What would be more scientifically interesting, would be if could do many do-overs and begin changing the world in many different ways. From politics, the judicial system, technology, and advance the human race in the 21st century. But on a more common level, I would strengthen bonds and possibly aid those that I had lost in my life. For sure, As I would want to go through another lifetime without them.