Question: What are all the ways to increase the readiness factor for the war with the Reapers?

Answer: 
As far as I can tell so far, the only ways to increase galactic readiness is through multi-player or either of the iOS Mass Effect 3 games.

You should be able to acquire enough military strength in game to where the readiness doesn't matter.
In multiplayer, play bronze and win to get about 4% added on to your readiness. You get much less if you die.

As for singleplayer, talk to people and do side missions.