You are going to die. Keep this in your mind.
Like how when a candle burns, it also melts. As you live you also die. With every breath our life dwindles. All of this will fade away.
I think it is very useful to contemplate the inevitability of our own death.
Remember that you are mortal.
Given the finality of death does what we spend our time doing, what we use our mind thinking about and what we care about really make sense?
We are all in one of two situations:
1. We will die young
2. We will live long enough to have everything we've known and loved torn away from us
We can't escape our fate, but we can make the most of our short time we have left. We can be happy right now and make others happy. We can resolve not to suffer in stupid ways.
I think the biggest lie we tell ourselves is:
"If X happens, I will be happy."
Why does X have to happen? Why can't you be happy right here and now? What's stopping you?
When you have X, you will then desire Y. There is no end to stories you can tell yourself about why you aren't happy. Why waste your mental energy chasing whim after whim when you could just relax in the present?
Given that we are definitely going to die, we should want to make the most of the time we have left. Continually reminding yourself about and contemplating your own death really does help put things into perspective.