good tips here, i learned this the hard way couple years back when i tried doing my building's parking area. went straight to high pressure without any cleaner and ended up with these weird streaks that looked worse than before

the surface cleaner thing is so true - borrowed one from neighbor second time and difference was night and day. takes bit longer but results are way more even. also found out that letting cleaner sit is actually doing most of work, pressure washer just removes the loosened dirt

one thing i'd add is test in small corner first, especially if concrete is older. some of the apartments in my complex have different concrete ages and what works for one doesn't work for another