I've made my first green triangle in Ingress. Here it is:
For the effort I have put in, I get +744 Mind Units (MUs) for the Enlightened faction. This was done while I grinded my way up to level 3. The game does get somewhat easier the higher you advance, but it also means you do a lot more grinding to get up to higher levels.
I'm not sure on the strategy to follow. Either I will let the Resistance faction take back what I have claimed, or I will defend what I have claimed. The game does not seem to have a definite path, except for the constant exchange of portals between the two factions.