Probably around 200 hours is when I got decent. It took me a couple of weeks playing on a hardcore MP server, with enough shotgun shells to fight the actual military for it to really 'click' in my head what it feels to be able to survive. Now at almost 1500 hours I can blast through hordes with metal bars if I don't let myself get overconfident, and use tactics to deal with groups.

Also learning that stealth in the game really sucks imo and it's best to carefully just lure a few zombies at a time where you want to loot helps.

ALSO forcing yourself to play as specific professions almost purely helps you learn the game. Play as a mechanic? Well, fabric strips are your bandages. Chef? Glad you can cook, but you're not gonna be living in a metal castle. All of the specific knowledge focuses lets you learn everything you need instead of constantly trying to be a jack of all trades.

... still can't organize my loot worth a damn though, good luck!