The common mistake I see a lot of people make when talking about Mass Effect is players saying they 'didn't know' there were options to save so and so or options to make 'X' decision.

Throughout the entire trilogy, there are pivotal moments that can have small consequences (such as an ally potentially turned away) but they can also have massive ones as well, up to and including wiping out entire races. With each paragon action taken and dialogue option chosen, you're earning points for 'blue.' This is the same with renegade, noted as 'red.' Both sides dictate how your Shepard reacts to certain situations and how others react to them. It's important to mostly dedicate your time leaning one way or the other right off the bat, especially early on in the game. Vice versa, as well, but you want to be careful not to lean too heavily into playing that middle ground. When you go paragon, there are renegade choices you must hit, it's tradition (punching the reporter, anyone?). While I encourage everyone to play the way they want to play, there is a caveat that you should at least be aware of, something that I've noticed many players aren't even aware of when the credits have rolled.