Thanks for the plugin tip.
I still feel like I must be missing something though. Since there are so many cues in sketchup -- axis color, "endpoint", "midpoint", "on face", etc. there must be a cue or guide I can use to keep me "on plane".

Hi,
Started learning Sketchup yesterday. I understand why objects cannot be pushed or pulled unless the lines are coplanar, but it's not obvious to me while I am drawing something, if the lines are coplanar or not. If I orbit around it after the fact I can see that not all points are on the same plane but for some reason, I can't tell while I am drawing. Any tips?