I've just been doing this job at the weekend. There were the common rust spots on my car, Roof front left edge in the gutter, and both back arch sills.
All I did was sand it down to metal, worked out the rust wasn't terrible, fill it in with filler (the usual golf ball to a pea) and I took my time on masking it up once prepped. Primer on, nothing special, more sanding, then more primer to build the layers. Waited for it to dry and put the first layer of topcoat on. Weekends work really. Leave it to dry for a week like I am currently. Then I plan to add another layer of the topcoat (blue in my cased mixed at a specialist paint place for about £17) and just spray the area smoothly basically and make sure it doesn't run.
Once I have finished that, I will use teacut to smooth the edges to blend it. I'll post photos if anyone wants. I've started the work but haven't finished it quite but I think it looks alot smarter than it did as It looked tatty before I did it.