What are the different ways to increasing your N7 number in ME3?
Increasing any class level in multiplayer (+1 for every level), or a bonus from promoting a max level class (which gives +10 N7).
By levelling your characters and promoting them at level 20.
The best way is on firebase reactor. Wait until your team members are in the reactor, then press the button near the door. Magic will happen, and your N7 will increase dramatically. Also people will love you