Get the weapon holster upgrades from the work bench. Runners are quick and you won't have time to dig into your backpack for everything. They suffer from the smart, because their dumb mechanic. Sound is their strength and weakness. The spot where you fired your gun or threw that brick is exactly where they are going to go. Remember, the vision is strictly line of sight in this game. The moment you break their line of vision, you have a chance to crouch and hide.
The strategy depends on the level, the numbers, your inventory, and your ammo. Separation and conservation should be your default strategy. R2 they shit and learn they routes. Hide in a spot where you can stealth kill once the chance is available. Close combat is very effective, but time consuming. It can take anywhere between 1 or 3 hits to kill infected. In a swarm situation, three hits on one enemy is three hits the others have to attack you as well. Always try to keep a melee weapon on you as well. These can be used for quick kills, but they loose that effect the more you use them. So just keep crafting them or swap them out.
Bricks and Bottles count as melee weapons too. Just equip them and press square as you would for a punch. Bricks go for three hits, while bottles bust after one. You can also toss the bricks/bottles at a runner to momentarily stun them for a few seconds, maybe 3. But it's long enough to grab and stealth kill. Also, melee attacks don't alert nearby enemies if they can't see the kill. Best of all, they're every where in the game.
Long as there ain't no clickers or bloaters around, guns blazing is a viable strategy. It's ammo consuming though and you're gonna need to keep on your toes. Their numbers can over whelm you in seconds. Shotguns, molotovs, nail bombs, melee weapons, and Shorty are the best weapons for that. You need to be able to get as many as you can at once. And/or have enough firepower to drop them or stun in their tracks with one shot. Standing your ground and letting them bottle neck can work. Pushing forward and letting them come to you works as well. Just make sure you're not flanked in the process. If you've got the flamethrower, just aim, and spray. Keep an eye on the fuel for that.
You can also stick and move. Use their echolocation against them. Sneaking to another spot to hide after each shot. They'll go to the origin of sound and search the area. Giving you a chance to set up that second kill. Bow and Arrows are one shot stealth kills, so they're great for this tactic. Sidenote, remember clickers take two arrows.
There are some parts of the game where you can just bum rush through the bitches. Do a quick melee attack to stagger those in your way and keep trucking. And if you got swarmed, remember to press the L2 button to break free of them and haul ass to a spot to collect yourself.
