As I was just flying on the advanced server and tower went offline it became a quick mess on Unicom in KSAN.
The idea of Unicom with other traffics inbound or outbound is to request traffic advisories. It is not meant for anyone to just take off and land on any runway they want as you have to take account of other traffic.
When you request traffic advisories the traffic in the pattern will tell you which runway they are using so you can adjust towards that.
After this all you have to do is provide your position, when you will take off / taxi and when you are clear of the runway.
It is not as difficult as it might seem but to keep it organized please follow this.