You yield to the person on your right.
If it's busy enough for everyone to arrive at the same time, somebody has probably just gone. That is the spark plug/tiebreaker. Whoever had that person most immediately on their right, goes next.
So if 3 had just gone, 1 is up. Then 2 goes. Then 4, then 3 again.
When you have a spread out intersection like this, sometimes someone goes, and someone else realizes they can move with no conflict, so they go immediately. Note that 2 can move almost the instant 1 goes, since no route of 1 can possibly conflict. 4 has to worry about 1 making an unsignaled left turn onto 2's road, but can proceed the instant 1 and 2's intentions are clear. 3 has to wait until 1 clears its road.
If things get confusing.... Then you fall back on everyone's sense of fair play. For instance, if you are the next 4 and as you sidle up to the stop sign, you plainly see that 3 has been sitting here "awhile", you surely know they go before you...