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

Answer: 
Readiness is managed via the [Galaxy at War](http://masseffect.wikia.com/wiki/Mass_Effect_3:_Galaxy_at_War) system and I'll go into the specific ways to earn readiness below:

Single Player
=============

[**War Assets**](http://masseffect.wikia.com/wiki/War_Assets) are the part of Galaxy at War you collect in Single Player. Simply purchase War Assets with in game money to earn varying amounts of readiness, rated by Military Strength. The wiki pages list the [Military Strength](http://masseffect.wikia.com/wiki/Mass_Effect_3:_Galaxy_at_War#Galactic_Readiness) of the various war assets. Some assets require certain conditions to be earned.

War Assets are not Readiness, but instead their effect (Military Strength) is multiplied by Readiness.

Multiplayer
===========

Playing [Multiplayer](http://masseffect.wikia.com/wiki/Multiplayer#Mass_Effect_3:_Galaxy_at_War) earns you various rewards that increase Galactic Readiness, such as [Promoting a character to level 20](http://masseffect.wikia.com/wiki/Multiplayer#Promote) or simply completing [missions](http://masseffect.wikia.com/wiki/Multiplayer#Missions).

Failure (any mission of any level): 3% Readiness  

Bronze Mission (success): 4% Readiness

Mass Effect: Infiltrator
========================

This iOS game will help you increase Galactic Readiness if you link the games. From EA's press release, via [Cult of Mac](http://www.cultofmac.com/145076/increase-your-galactic-readiness-with-mass-effect-3s-ios-companion-app/):

> 
> Inspired by the deep and immersive Mass Effect 3 universe, in Infiltrator players will help to free prisoners from a hostile Cerberus base and will receive rewards for collecting evidence of Cerberus’ crimes along the way. **Every completed rescue and intelligence discovery in Infiltrator will increase a player’s Galactic Readiness rating directly through the Galaxy at War system in Mass Effect 3**.
> 
> 
> 

It's now available for Android as well: [North America](https://play.google.com/store/apps/details?id=com.ea.games.meinfiltrator_na) and [everywhere else](https://play.google.com/store/apps/details?id=com.ea.games.meinfiltrator_row).

Mass Effect Datapad
===================

[Datapad](http://masseffect.wikia.com/wiki/Mass_Effect:_Datapad) is a free iOS app that will allow you to monitor your Galactic Readiness and a minigame which will allow you to slowly increase it. From the Galactic Readiness map you can send select 3 different mission points within each sector which can earn up to a 1% readiness boost for that sector only. It takes anywhere from 1 hour to 6 hours to earn a point. You can increase this by getting various power-ups based on points earned playing.
The only two ways of increasing readiness is by participating in Multiplayer, and by trading in Intel from MEI (Mass Effect: Infiltrator).

MED (Mass Effect: Datapad) is a FREE app which allows you to view your Galaxy at War.
Which in turn is split into 2 things, Strength and Readiness.

I have explained readiness.

Strength is increased by you war assets in single-player, which in turn is multiplied by Readiness.

The better Strength/Readiness you have the better the ending is (Although i don't know what it is I've heard it sucks). Still if it sucks, why get one which sucks more :)

Unfortunately i don't know the specifics of percentages or whatever as i do not have the game yet, however i hope to be the proud owner of a copy soon :D