One of the important things to do to get this trophy is to first decide on which route you're going to play, a Paragon or Renegade trophy and add points to the charm or intimidate skill.
Next a good assignment "side mission" to do is Wrex: Family Armor as this helps during the conversation you will have with him on Virmire. Otherwise you will need to boost your charm/intimidate score to 8 or 9 to ensure you can pick each option.
To do this along with the occasional skill point and free spectre skill how you answer to previous conversation can also have a benefit of +2 or more paragon/renegade points.
You can search online for Mass Effect: Morality Guide and it will give you a list of the choices you can make for your character and how much points you get for each answer.