How to coordinate with the sun
A very simple, but good way to coordinate:
Are you look at the sun or not is a very important thing if you want to find to your friends. You should always go in one direction.
The sun rises in the east and sets in the west!
How to coordinate with the street
Probably the most efficient way to coordinate.
If you're at a street, go and look for "Not-Player-made-Buildings" to tell your friends where you are. (works perfect together with the online map)
How to coordinate with airdrops
Its the best way to find your friends if you're nearby them:
On a normal Rust Server with a lot of Players comes a airdrop every ingame-day. If you tell your friend from where the airdrop came (from your position), you'll have it much easier.
The water can help, too!
Water is only in the south and west edges of the map!