During conversations mainly use the bottom right hand dialogue selection and if you're intimidate skill is up high enough use the bottom left selection (red text) during dialogue for maximum renegade points.
A couple high gain renegade areas are:
1. Feros: When coming back from killing the Thorian, do not use the gas grenades, but instead kill ALL the colonists, if you get them all I think it will net you 32 renegade points.
2.Noveria: After helping Lorak Quinn (sp?) to get the garage pass, the internal affairs lady will want you to get him to testify. Forcefully make him testify and you will get 25 renegade points.
3. Noveria:(Main Plotline) If you decide to kill the Rachni Queen rather than save her, you will get about 25 renegade points.
4.Virmire: When confronting Wrex, simply kill him. +25 Renegade.