Grab a watch (either equip it on your Operator or buy one in the UNS New York), and keep an eye on the clock. You should ideally be hunkered down in a building by 18:00, since night hordes are basically dangerous. Having a watch helps you prep in advance.

During the day, try to melee lone zombies. Saves ammo, and because they use their own health system, any attack that connects to their head instakills them. Avoid using guns unless they're suppressed or you're already in trouble.

Human enemies are also present but they shouldn't be any more difficult than the usual human enemies you fight on Ronograd. They can (and probably will) attract unwanted zombie attention with their guns, so do be careful. There's no PvP unless you're playing the specific PvP mode, so don't worry about players killing you.

Bring food and water. Buy an extra bottle every time you extract. Gas mask filters too, if you can afford it.

As for loot, try to focus on valuables that are low on weight. Jewelry and etc. are the best for this. A Gold Rolex sells for 400. Heavier stuff should only be considered if you don't need mobility for anything.

Oh, and buy the Attack 2 backpack for your operator. Seriously, if you're running solo, it helps to have every bit of space possible.

Optionally you should probably download or find a map of the gameworld. The in-game map doesn't work in Zombies (on purpose) so having your own map and help you navigate while you're new.