Haven’t finished Mass Effect 1 yet? You should. Thinking about replaying the game before Mass Effect 2 hits next week? That’s not a bad idea. Mass Effect had enough plots threads that it's worth a refresher before you hop back into the universe. Not to mention that you’ll want to have completed the game if you want Mass Effect 2 to read your old save file and reference all your old misdeeds. Fortunately, BioWare writer Mac Walters is here to walk us through what to see and do in the first game before you unwrap the sequel. Take it away, Mac!

So you’re playing Mass Effect right now and you’re wondering, “Do any of my choices really make a difference?” They do! “But how do I know which ones?” While I can’t catalog everything, I can give you three simple rules to follow if you want to make sure your decisions count in Mass Effect 2.

If you’re in a position to decide whether someone lives or dies…think twice. There’s a good chance your decision will be reflected in Mass Effect 2.

If you’re wondering whether or not it would be a good idea to punch, kick, or otherwise abuse someone during a conversation, again…choose wisely. The denizens of the Mass Effect universe have long memories.

If you’re followed and harassed and otherwise irritated by a well meaning though slightly unbalanced sycophant…you guessed it: choose your reaction carefully. Sometimes the people who love us most, hurt us the most deeply.

Mass Effect is about people and the stories surrounding them. Naturally, the way Shepard treats these people will greatly impact your playing experience in Mass Effect 2. There are some obvious decisions that hold serious consequences for Wrex, Ashley, and Kaidan on Virmire. (It’s a planet full of tough choices – remember Captain Kirrahe?) And there are even larger decisions to come. At one point, the lives of the Citadel Council will be in Shepard’s hands. Will you let them live or let them die to make way for a new Council, maybe one that better represents humanity?

And of course, there are your squad members. Naturally, you’ll want to make sure you collect every one. (You’ll never be able to culminate that krogan romance if you leave Wrex behind on the Citadel.*) When you meet your former squad members in Mass Effect 2, they’ll react differently to Shepard based on how they were treated in the first game. And… keep in mind that not only do we track these changes in Mass Effect 2, but we continue to track them as we begin work on the third game in our trilogy.

Mass Effect is a universe filled with choices. How will you play it?

(*Do NOT try to romance Wrex...he’s not into it.)