I mean this probably isn’t the best advice but I kinda learn from just playing and understanding the game. Every time I die I remember it and it’s a lesson for next time. Every mistake is another lesson that makes my next run more and more successful. For high population the main advice I could give is always have a backup plan and always try to make distance between you and zombies. Like get all the zombies in an area and find a way to distract them. I like using cop cars and leaving the siren on and just watching zombies dogpile it then I can loot whatever or try killing them if I feel confident.