trouble using bondo

I'm taking an auto body class and this is how we do it.
Spread your filler over the weld area. Sand with the flattest longest sanding block u have and 36 grit paper. Fill in low spots with a bondo / filler skim coat and repeat block sanding with 36 and long block.Then mix up new batch of filler with Plastic honey to thin out filler or use body glaze (Honey and filler mix gives u more work time than glaze)and skim coat to fill in 36 grit scratches. Sand with 80 grit and a hard block. Prime with Surfacer/high build primer,guide coat and block sand with 220 grit paper wet and hard block,re prime,guide coat and sand with 400 grit wet. Make sure that your mixing board and spreader are clean and have a burr free edge on them before doing final skim coat.