Sometimes it seem like "nothing" is used today. People just start writing code. This actually isn't a bad way to go 70% of the time. But if you find yourself struggling it might be time to step back and think it out with some informal UML sketches. Nobody uses "formal" UML anymore.

The main risk of UML is it can lead to overly complex designs - it is so easy to add another box and arrow, to make it match a GOF pattern, etc.

As for what we use here in practice today - pairing and talking out ideas sometimes with informal UML sketch, and test driven development.