I mean, short answer, GIT GUD.
Long Answer, know the monster's patterns (i.e. when archviles use their magic take cover, dodge the revenant's missiles), know what weapon will be useful for a map, don't just spam the BFG just because you have a BFG, doesn't mean you should use it all the time, take advantage of Monster Fighting, and prioritize the biggest threat in a map( If there's a Pain Elemental or an Archvile, you better make sure you hit them first, before they become dangerous).
Also if you die, think about why did you die and what are the thing that you should've done to prevent that death, and if you die and blame the game, it's mostly, your fault.
Also don't just play UV first when you play a WAD for the 1st time, go for Hurt Me Plenty first, then if you're confident enough, go for UV, there will learn most of the enemy placement from HMP and then some.
Also watch some DOOMERS's videos, they are useful, trust me.