The first minute or so of gameplay is death-decider number one. Is there or is there not a zombie creature immediately outside your spawn? If it’s anything but a zed dog, you’re better off just starting over. Zed cougar maybe. Zed bear? Nah. You’re done. Start over.
Left 4 Dead is a pretty awful example of zombie survival, because everything in it is the opposite of what you’d want to do. In reality, you would want to stay way the fuck away from zombies until you are damn sure you can handle them in a fight, and even then you avoid it when it’s anything but completely convenient. If you can’t brush it off, stay away.
When I’m traveling, I toggle Safe Mode on so that I can both move quickly and be alerted the instant that something dangerous appears on the edge of my detection radius. Generally you can see a bit farther than most enemies, so if you catch sight of, say, a rogue zombie bear, step back again and try to go around them. If you get a thin perimeter of tiles filled with enemies, you might have to bait one in and use that opening. If they’re all going to kill you, well, I guess you can go the LONG long way around, or just find somewhere else to go.
Basically, you handle no engagement you aren’t positive you can win. Scavenge at night, pay really close attention to where things are, and be a slippery little eel when they start to notice you.
It’s gonna take a while. After some time, though, you’ll be fully armored up and you’ll be able to safely handle zombie bears and then start to look at some of those robotic sons of bitches next. All just a matter of careful progression.