How to Choose Ganesha Idols

I have heard a lot about choosing Ganesha but never a reason as to why it should be chosen in that way...
Right sided trunk or left sided trunk Ganesha to choose and got an answer for this doubt with satisfactory answer that one should choose Ganesha with trunk curved left... from this beautiful blog...

Symbolism of Ganesha

About Ganesha yantra you might read at Sanatan society