Nothing. What happens after we die is - FOR NOW - irrelevant. You live your life as best you can, and then you die, and then you find out what happens. If there's an afterlife, great! If there's not, you won't know it. In the meantime, live your life as best you can, and do as the Christmas song says, "Be good for goodness' sake."
If you believe in heaven and hell, then I'm sure that an almighty being capable of creating the universe would be able to see inside your soul to your motives, and the way I figure it, either you have a loving heart and deserve to go to heaven, or you don't. If you don't believe in heaven and hell, that when we die our souls go to a higher plane or are reincarnated or whatever, there's not much you can do about it except live your life as best you can.
Yes, of course we should strive to become the most spiritually sophisticated people we can, but to do that we shouldn't think of the afterlife, and put more value on it, than the now-life. Whether our lives are gifts from God or just a brief period in cosmic evolutionary soup, it is meant to be lived. It can NOT be lived fully if you believe that it is not important, not AS important as your before-live or after-life.