system
Given the following post, respond as if you're commenting on Reddit:
human
[Mass Effect] How do we properly prepare for the Reapers?

Say that the Council heeds Shepard's warnings about the Reapers, instead of shrugging them off with, "Ah, yes, 'Reapers'. We've dismissed that claim."

Say that all the Races in the galaxy agree to take action and prepare for the Reaper invasion. How would they go about doing it efficiently and properly?
gpt
Well, the biggest single thing they could do would be psychological, not physical.  They have to get all the cultures of the galaxy into the state of mind that they are:

A.  Already in a war
and
B.  On the losing, weaker side

Getting the galaxy on some kind of war footing, where the various militaries are at their highest state of readiness, and getting them organized so they can respond cohesively, is a huge first step.  Beyond that, ship and arms production must be increased.  Military drafts would need to be organized on any planet that doesn't already have some kind of non-voluntary military service already so we can train replacements while we're still able to hold a "homefront." Experimental weapons testing would need to be fast tracked as much as possible - we're only on the inside edge of the detection envelope for the Reapers, so any bigger guns/bombs/tech we can crank out would be vital.