First of all, don't sit next to plots all day. It's simply a waste of time and makes you even more frustrated when you get unlucky and someone else clicks it.
Second, check for free plots from time to time, stay for like 10 minutes and then leave.
With the current system it's all random. Or you get lucky or not. If not, try another time.
Spend time on things that you enjoy more, than mindlessly clicking on a placards.
Don't stress yourself, it's unhealthy.