User blog comment:Oskar 73/Is there an effective and coherent ME1 Guide?/@comment-7100064-20130430004223

Talking to them is kind of unlocked by doing story/secondary missions. There can be certain things that change based on how you talk to them. For example Garrus can be pushed between Paragon or Renegade based on how you talk about Spectres versus C-Sec which a bit of the time more is about if Spectre should skirt the law and and it's right.

As for stuff like those missions for Tali, Wrex and so on. You can visit a few of the planets ahead of time and the areas to enter to for missions like Wrex won't let you go inside until you have the mission. You should have ample time talk to Wrex and then do his mission before it's too late.

Just do not go to Virmire until you completely done with any missions you wish to do ahead of time. Recruit everyone you can before Virmire as well. That planet has some deciding factors for you.

Roleplaying games tend to have main story cut offs. For Mass Effect they are Priority Missions. Virmire is the primary point when there is no going back in ME1, For ME2 it's Acquiring the IFF. ME3 Kind of has a couple and is split more into Acts than the other two.