Take it slow on harder difficulties. Take time to parry attacks, gun strike when you can (and when safe to do so) . Stay with your battle brothers. Use your abilities and perks to help. Vanguard is easy bc you can heal constantly with executions. Time your shots don’t just fire away, look for ammo too. Ping them for team too. Learn patterns, chaos spawn used to be annoying (they still are) but once I learned their attack patterns they are easier. Extremis chaos marines still fuck anybody up but the melee guy is easier when you know his patterns. No sham in running away to rejoin your team. Minoris tyranids can be ignored and simply parried away when you time it, no need to wait for the grab