Ditto on the previous posting. As a general rule, daytime nets are held on the 5-meg or just below frequencies and just above 40m.
Evening nets are generally found on both sides of 75/80m as well as just below 40m. It all depends upon what has been allocated to each particular state.
There are a multitude of other allocations, but they may or may not be used in your area.
As for what group to join? There's only ONE!!!
Lon - NNN0OOR/NNN0GAW THREE (W3LK)
MDE Navy-Marine Corps MARS
Proudly serving those who serve!