How to have a clear mind

As human beings, we don't know where we come from and where to go after death . The creator(God) gave us his spirit , so his spirit dwells in us no matter which religion we belong to and he also gave us the brain to decide what is good and bad , so we have two inclinations in the brain that is -the good inclination and the bad inclination.Using a good inclination will make you live long .for example -have a positive mind and a clean heart that's all this will make you live long