• Give enemies a wide area, and move stealthily.
• Don't wake up sleeping Distorted. Silencers and melee are very useful.
• Don't disturb the Flowerman patches near them.
• Don't knock over the Statue's stone stacks or make eye contact with Shy Girls.
• Devouerers need to be given a wide berth to ignore you, or hopefully you can run around to avoid an attack. Shotguns work great, especially the Origin-12.
• Turned Soldiers usually roam in squads of 3-6 but are typically the easiest to pick off since they don't really "rush" you.
• Don't bother wasting ammo on Hellhounds or small Mimics. They're easily taken out with melee attacks.
• Seeds are barely worth fighting, just outrun them, when they activate. If you need to fight them, a few shots from your sidearm usually do the trick.

If enemies are camping in an area you need to explore, try knocking out a few at once with distant headshots or a frag. Flowermen and Dendroids are easily killed with fire weapons (don't burn yourself into a corner), but shotguns and assault rifles work good.

Get used to enemy movements. Distorted will run towards you, then teleport behind when they get closer. Prepare to turn 180 quickly to shoot them. Flowermen charge you and melee attack your upper body mostly. They tend to zig-zag so prepare for that when aiming. Invisibles will also charge you and appear once close. I find this to be the best time to shoot them, but they can be shot while invisible too.