Why does my car still show marks after I wash it?

I have had a lot of time on my hands during the lockdown and decided to give the car a good clean. It's metallic black so shows up virtually any marks. No matter how careful I am, the bodywork has marks...

What's the best way to give my paintwork a makeover?

I have just bought a Ford Mondeo on a 60 plate. I'd like to give the paintwork a bit of a makeover - it's not bad but needs freshening up a bit. What do you recommend?