Even before I had a foamgun, I gave the car a full pre-wash rinse. This is with a light but high pressure mist to break all the large stuff off. Then it gets a thorough "sheeting" rinse to make sure all the loose stuff has completely slid off of the car. My prewash rinse is a good 5 minutes.
Next is a complete foam cover of the car on all sides. I then start working it one panel at a time:
- Spray foam on working panel, spray a small amount on sponge or mitt.
- Clean panel, rinse sponge/mitt, repeat for next section.
I definitely go thru more soap than a normal two bucket wash but I get Meg's Gold Class for 1.25 gallons @ $8 at Costco. It doesn't get any cheaper than that for a good soap. It's worth it in the end if I prevent swirls.
For my minivan's roof, I use a mf chenille patterned wash pad on a pool. I only push the pad around. I don't put downward force of any kind...I just let the weight of the wash pad do it's work. I put the foamgun to it's middle setting and really lay it on thick. This is to ensure I get good gliding of the wash pad but also so it doesn't dry before I'm done (no shade at my house so I have to work in sun often.)
It was so hot this past weekend that I found that I had to constantly re-wet the car and van. I used the quick "foam shutoff" lever on the foam gun to switch between foam and water only.