So, as I've been playing this game for a bit (15 hours or so) now I'll share some things I found useful:

Most importantly: try to make friends asap, it's easier as a team/group. Go on a teamspeak/skype to make life easier.
ALSO: See an enemy (with a gun)? RUN FIRST, then chat in AllChat (right top corner - chat button) and ask if they are friendly. Many people (including me sometimes) shoot on sight - just because they don't want to get shot themselves (Hi Rust!).

Use the car as much as you can, although handling it might seem difficult at the start, with the car you can:

- kill NPCs - loot them
- drive against trees - gather wood
- drive against animals - get food to put next to your campfire (crafted)
- remember where the cars spawn
- when you have enough wood (forst in the middle of the map) try and build a garage (2 doors so car can go in/out)

Protect your goods:

- Dont go in the most populated area at the start. You will face unfriendly players there.
- use the given buildings and insert a door e.g., preferably buildings which have lootboxes inside so you can store things
however: people see that the building has been taken over and want to break in.
- Make more layers to your building (e.g. 3 doors in a row. It takes more time/effort to destroy 3 doors/fences)

So:

- use the shovel and hide things. Doesn't have to be in the building, but at a spot you can remember and can access savely (without being seen/killed). Sometimes hiding in "plain sight" is the best option after all. It is easy to share items this way, too.

Get basic armor (crafting)

Don't walk on the streets, but next to them - or you will get hit by a car at some point

Deny items from other players - build doors around loot boxes