How do i write a good descriptive piece about a apocalyptic world

I can't imagine.

Yeah, makes me kinds sic too.

Start by placing your thoughts in a dreary, dark, horrible place. No electric, no plumbing, no way of getting gasoline for whatever vehicles may still exist, no form of heating apart from natural (think of chopping wood). Homes with windows blown out, walls ripped off. Rubble everywhere.

Imagine all these things and then place them on your sheet of paper (or in the computer).

Try to decide what sort of rule there is. Is it a group of roving and marauding gangs or a singular tyrannical leader?

How will you acquire provisions (food, clothing)?

The thought process for creating this is all within you, inside the crevices of your brain (unless of course the apocalyptic world is being ruled by zombies, in which case part of the brain may have become a midnight snack).

Best of luck and let us know how it turns out.

Also, consider taking a peek at Strunk and White.

Firstly look at the logistics of things. Who survived? What did they survive? How did they survive it? how are they getting food and water? who is in charge? etc. etc.- if its not at least logical, its not believable and if its not believable, then the 'magic' of it all is gone
Then focus on embellishing it with imagery and language techniques. When doing so focus on the ideas of death, barren lands and sorrow.
"The whole world had been silenced in one motion, like breaking someone's neck but without the mercifully quick departure"
"He looked at his hopes, staring into the darkness of space. His hopes had been burnt to the ground and left as cold and lifeless as the earth he now stood upon"
Those aren't great but im sure if you take some time you cant make something that sounds way better

Also use longer, more in depth metaphors to lengthen your sentences and by the way its an apocalyptic world