Bethesda's return to hell is plenty challenging so some Doom Eternal tips will be a welcome way to ease your way in. This is a general guide that covers the basic of combat, exploration and upgrading your way through the game. There's no way of making all the actual ripping and tearing easier but we can at least help you not make any mistakes that might make things harder.
1. Never stop moving in combat
This is Doom 101. If you stop moving, you'll end up as dead as the corpses littered around you in hell. So always make sure you're moving across arenas, using the poles littered around the vault over enemies, as well as the blue energy strips that will launch you up in the air or across an arena. There's a whole variety of power-ups scattered around, from health and armor to extra ammo, so it also makes sense to haunt those out while you're taking on demons. It could be the difference between a successful rip and tear or an ignominious end.
2. Always use Flame Belch on a Glory or Chainsaw Kill for extra armor
The whole schtick with Doom Eternal is doing horrible things to demons to get the stuff you need like ammo, health and more. When you unlock the Flame Belch (which is basically a flamethrower with a weird name) it lets you get armor by burning it off enemies. You’ll get a little over time from burning creatures, more if you damage creatures on fire and the most if you kill them. Because both the chainsaw, which gets you ammo, and Glory Kill, which gets you health, are basically insta-kills, always Flame Belch an enemy before you perform each move to guarantee your armor never runs out.
3. Stop and look around for secrets when it’s quiet
There aren’t many quiet moments in Doom Eternal but when there are, stop: look around, check the map. There are plenty of secrets and hidden areas and it’s easy to miss them because the whole game is heavy on the running screaming through bloody chaos. It’s both easy to forget to look, or to run on to see what’s next and lose access to the area you were just in. You can replay levels easily enough but maximise you time by taking a breath and investigating when you can. Look for cracks in walls that aren't lit up green, and if you can see something you can't reach check the area it's in, and the map to try and work out how to reach it.
4. You will be able to find all the secrets in a level with your current gear
Doom Eternal is loaded with secrets and collectibles, but it's not a Metroidvania. You'll never need to backtrack to previous levels in order to find all their goodies. It's possible to collect everything in every level on your first attempt. You might need to progress further in that level and collect a key before you can reach certain secrets, but you'll never need to outright replay the level. Keep tabs on your map and, before exiting each level, fast travel to earlier areas to mop up any lingering secrets.
5. Make the effort to find extra lives
Extra lives are incredibly valuable, so you shouldn't waste them. Let's say you have two extra lives when you start a fight. Things go horribly wrong - as they often do - and you burn through those lives in an instant. At that point, you may as well load your most recent checkpoint and restart the fight. You've barely made any progress anyway, and if you start from scratch, you'll not only get your lives back, you'll also have a better idea of how to handle the demons in that particular fight, making you less likely to use an extra life. Checkpoints are pretty frequent, so you won't go too far back by loading one. Try and save your extra lives for when you really need them, like in Slayer Gates.
6. Explore the Fortress of Doom
Doom Eternal has its own hub level, and like any good hub level, it's filled with useful collectibles. You can use Sentinel Batteries to open doors around the Fortress to unlock weapon and suit upgrades, skins, and other niceties. You'll find any Easter Eggs you've collected displayed on the hub's walls, and there's even a practice arena downstairs. In other words, don't get tunnel vision with the level selector. There's way more to the Fortress of Doom, and it can really help you out.
7. Spend weapon points when you get them
You earn weapon points whenever you clear an arena, challenge, or Slayer Gate, and you can spend those points immediately. I'm talking the second you get them - just pause the game and upgrade away. That being said, it's worth keeping track of how many weapon points you have and how many you need for your next upgrade. If you've got four points and you need six for, say, the Super Shotgun reload boost, you know that you'll be able to buy that upgrade after two fights. Don't let those weapon points gather dust; spend them as soon as you can.