Prepare for your next life the same way you prepare for tomorrow. Unless you willfully manipulate your sleep pattern you will not experience the concept of 'tomorrow' earlier, in the same way that you will not reach the afterlife earlier than intended unless you end your life prematurely. To not prepare for the next life is equally narrow-minded as to not prepare for the future days in this life. Just as you try to secure the survival of your physical manifestation the upcoming days, weeks and years in this life, you do equally well to secure the survival of your spiritual being in the upcoming lifetimes. To not believe in it means that you have no interest in the upcoming lifetimes, which is equally naive as to not believe in 'the tomorrow', despite the fact that you have reached 'the tomorrow' more times than you are able to remember in only this lifetime; remembering is hard, most cannot remember their early childhood and definitely not their earlier lives. And based on this they neglect the opportunity to evolve their spiritual being which causes them to slowly die from within through the lifetimes. Just as there is a hierarchy of dominance in the physical realm, which can be climbed through the days by careful planning of tomorrow, are there also a hierarchy of consciousness which can be climbed through the lifetimes; although most in the bottom of this hierarchy cannot remember or understand this due to insignificant spiritual strength.