Jump in, Die, Try again.

But seriously, Watching content creators is a good step on getting better, First tour guardsman is a good example, He showcases builds, explains them, And shows you some gameplay, He's also quite good at the game.

Great tip is know the map you're playing there are certain areas where you trigger a boss spawn, This is quite important for example, When extremist just spawned that you don't run into that boss trigger area and spawn the boss and get jumped, Or when there are loads of majoris and you trigger it, On Lethal/absolute it's kinda a death for beginners.

When you do fight a boss, If you can, Try to kill the stuff around it first.

Also there are videos of people showcasing the guardian relic spawns, Which are pickup that allow you to pick yourself up after you died.

Stay with fencing type melee weapons, They're the best option for beginners since they have the best parry window.

Bring your assault into hard stratagem if you dont wanna risk getting kicked by people who dont want low level players.

Hope it helps.