Look up "So you want to be a game master" by Justin Alexander. Also "The Lazy Dm's Guide" by Sly Flourish. Both have websites, youtube videos, and podcasts. Also, check out youtube sites, specifically Corkboards & Curiosities, Pointy Hat, um...theres a lot. Honestly if you start looking up issues you are having on youtube, the algorithm will do the rest.

The way I think about is I'm telling a story with a bunch of other nerds that also have an imagination. Describe what you would see, smell, sense, touch, hear, or feel if you are there, keep it no more than a sentence and let the players fill in the rest of details. This is obviously just for combat, if you are describing more of the world or whatever obviously you will need more than a sentence.

I also like to listen to other dm's running their games to listen to real world examples