Removing surface rust help/question

I've got some surface rust spots in various places that I've started taking care of. It's my first time doing any body work and I'm a bit confused as to how I should start taking the one of the front fenders down to metal.
I'm using a da sander with 80 grit and I guess my question is how should I be using the sander on an area that isn't flat?
Should I just try to use the sander at an angle and use the edge of the sanding disc, or what?
Probably sounds a bit stupid, but I'd just like to try to do it right the first time and I don't have any experience with this.
Also, just to get the areas with surface rust down to metal, I should have the spindle lock turned so the sander is in grind mode?
After I've gotten far enough down, I plan on using some naval jelly and steel wool.
Thanks for the help, really appreciate it.