Start with the smaller hordes around belknap and cascade, they're perfect for getting comfortable with the tactics. Chicago chopper and auto shotgun are your best friends here, plus make sure to grab those napalm molotovs when you can. During daytime the freakers bunch up in caves and tunnels, making them easier to track, but night fights give you more room to maneuver. Good tip about those attractor bombs they're absolute lifesavers when paired with proximity mines.

Most regions have around 10-15 hordes, and you'll want that stamina maxed before taking on the bigger ones. Iron butte and lost lake have some nasty surprises, so maybe interesting to thin out the smaller groups first before story missions force you into the tough fights. The sawmill horde is particularly brutal with 500 freakers, definitely save that one for when you're fully geared.

Watch out for those story-related hordes like chemult station though, they'll reset if you try them too early which can be pretty frustrating. Once you've cleared about 80% of them, you'll unlock the mg55 which makes the remaining hordes way more manageable just remember to keep moving and use the environment to your advantage.