I did this in my driveway... I just used a few things for reference... i used a tree I could see in my rear view mirror.. you shouldn't be able to see that on your side mirrors.. b/c if you can see it in one mirror you should use the others to see other things.

I point the side mirrors more at a perpendicular angle with the car so I can see the lanes next to me.. not behind me.

So far it has worked really good. As soon as I see a car disappear from my rear view mirror they appear in my side view mirrors.

I am extremely confident with how I have them.. but I always do a quick glance b4 changing lanes.