I found using clay makes a huge difference.
Do it after you wash the car, but before you polish it.
I do find it can be fiddly to use if you're using actual clay, however the place I work at uses a clay bar mitt which makes the whole process so much easier and quicker. I'd really recommend one.
https://www.amazon.com/AutoCare-Surf.../dp/B01KWOM0HY