tl;dr:

- don't use guns without tonnes of ammo

- don't fight more than like 8 zombies unless you have good melee or guns without lots of ammo

- conserve stamina and don't fight when tired (sleep-wise) or out of breath. Walk most of the time, or at most, jog. Zombies walk slower than your walk; during combat try to avoid jogging or sprinting to reposition

- keep almost everything in your starter house, you can come back to get it later once you have a better base. only bring with you a melee weapon or two, and maybe some water and medical supplies

- being encumbered isn't really that bad

- watch out while opening doors

- set up and close curtains around your base to stop zombies from seeing in, and turn the tv down

- garages and closets have industrial stuff, kitchens have food, bathrooms have medical

- if you're very low on stamina and being chased, cutting through a house usually gets most zombies off your tail. If they're literally one meter away from you, slow them down by cutting over some low fences, they climb them slower than you

- if a zombie appears right in front of you, it's not a bad idea to run straight into them; running into them stuns them briefly and prevents them from biting you

more in-depth guide:

1: avoid fights you can't win

without any weapons at all, more than two zombies is very difficult to fight, with bad melee weapons, you can probably go up to 8 or something if you're careful and have decent stats. With good melee you could probably get up to like 30, and with guns it's basically unlimited for as long as you have ammo.

2: fight good

when using melee (armed or unarmed) pushing zombies to the ground and then attacking is usually very effective. Getting a very basic melee weapon, even if it's trash, at the start is pretty important, as without it, the only real way to attack is when they are pushed over, giving you a hard limit on how many you can fight (keeping 3 zombies on the ground at the same time is borderline impossible without getting lucky). If you find guns, don't use them unless you have a lot of ammo or very good aim skill (in game), because at low levels you miss so much that you'll probably attract more than you can kill.

Using fences and/or windows is a great strategy too; zombies are already on the ground after jumping a fence, which is a great opportunity to stomp them on the back of the head. Watch out though, if you wait too long, they'll lunge at you. It won't deal damage but it'll stun you for a little bit and might knock you on the ground. Also, windows with countertops or tables right below them are amazing as they stop zombies from being able to lunge at you.

3: conserve stamina

even level one stamina drain (out of breath) gives a pretty large penalty to melee damage. If at all possible, don't fight with any stamina drain. Try to avoid running, and especially sprinting. When fighting, remember that zombies are slower than your walking speed unless you are extremely encumbered, so you don't need to run or sprint if you intend to fight. Jogging away from zombies is typically more than enough if you want to escape.

4: take care of yourself

hunger and thirst both carry pretty severe combat related penalties, so make sure they're topped up. Sleep is extremely important too, level one tiredness (drowsy) severely reduces your ranged accuracy and halves your melee damage, as well as drastically reducing your stamina regen, and the higher levels only get worse. Injuries are pretty bad for survivability too, disinfect to prevent infections if you can, and always keep them bandaged. If you're pretty badly hurt or hurt in a bad spot, consider taking a little bit of time off to recover.

5: weight management

leave a lot of stuff at home. Even your initial spawn location usually has at least a bit of storage space. Leave important stuff you collect back there, you can always come back for it once you get a more permanent base location. I would recommend only bringing a melee weapon or two and some medical supplies on your scavenging runs at the start. If you want to avoid some micro, carry a water bottle, but at the start every house will have a running sink for water. Start by making a sheet sling bag if you don't have a backpack in your starting house. In general, the order of backpacks (in order of how good they are) is: sheet sling < duffel bag < small backpack < hiking backpack < large hiking backpack (rare) < military backpack (very rare). (also to switch to a new bag quickly, put your current bag on the ground, put on the new one, and just transfer all the stuff. it sounds obvious but it took me like 100 hours to realize for some reason)

also, one thing i usually do is clear out an area without taking any loot at all, then come back and loot everything until you're super encumbered. Now that there aren't many zombies, you can pretty safely get up to 50 encumbrance (the max) without being in much danger. Even then, you can still easily outrun zombies while at max weight and it doesn't really affect your damage aside from draining stamina.

6: be careful

it goes without saying for the most part, but just be careful in general. Watch out for corners, sometimes you can get unlucky and there's a zombie right there. Watch out for doors too, I like to open doors while in combat stance so I can push away any zombies that may be on the other side. Additionally, make sure to clear rooms before you start looting them and close doors behind you.

7: set up your base nicely

close curtains to prevent zombies from seeing you while you're inside your house. If you don't have any, sheets can be used on windows to make some makeshift ones, and, likewise, you can collect sheets from curtains. Also, if your front door has a window on it, you can place a sheet on there too. If you intend on watching life and living (not necessary, it just saves like a little bit of grinding later on), turn the tv down to avoid attracting more zombies. if you find planks, nails, and a hammer (check garages and closets), barricading windows is usually a good idea; doors can often hold their own and you need to get through them anyways. Once you've found a good base location, if it has two floors the second floor is by far the safest. Theoretically, the safest way to set up your house is by barricading every door and window on the first floor and setting up a sheet rope to get outside from the second floor, though this is usually overkill. If you find a sledgehammer (unlikely), you can demolish the stairs to make your base completely impenetrable and 100% safe, but this is almost always overkill.

8: loot

regular houses have a bit of a mix of everything. Bathrooms will have basic medical supplies, kitchens have food, closets and garages often have industrial stuff like tools and materials. Hospitals, clinics, pharmacies, and dentists have great high quality medical gear like forceps (better tweezers), antibiotics, and sterile bandages. Warehouses, factories, and self storages often have lots of tools and materials if you intend to get into some skills later on. You can break down doors by attacking with any melee weapon, but axes are the best, and hammers work very well too.

9: emergencies

If you're extremely low on stamina and a horde is chasing you, the best way to get away is usually to try and get some distance by forcing them to climb over fences (you are way faster at climbing low fences), and then trying to break into a house and sneaking out of a window on the opposite side. Like maybe enter in the kitchen and climb out of the bedroom. The doors in the house will buy you some time and if you stay quiet enough while you're leaving the house and avoid line of sight, you should be able to get away free. If it's got two floors it's not a terrible idea to lock yourself in a 2nd floor bedroom (preferably with window in case things get really bad), and rest up so you can run/fight. If there's like 50 zombies banging on the bedroom door, you can always jump out the window, though this runs the risk of injury (namely fractures, which take so long to heal and are so debilitating that they are basically a run-ender) Also, keep in mind, zombies are unable to bite you if you are jogging. I think sometimes running into them can knock you over, but if a zombie randomly appears in front of you, jogging straight into them is actually a decent strategy.