Really depends what you mean by 'catch up'. How much of a completionist are you? By and large, release order is a safe bet. If you're thinking purely in terms of the current, ongoing saga with the Mandalorian, I'd probably say something along the lines of

Original Trilogy (A New Hope, Empire Strikes Back, Return of the Jedi, films IV-VI)
Prequel Trilogy (Phantom Menace, Attack of the Clones, Revenge of the Sith, films I-III)
Star Wars: The Clone Wars (the CGI series, specifically)
The Mandalorian, seasons 1 and 2
Star Wars: Rebels
The Book of Boba Fett
The Mandalorian season 3
And then the upcoming Ahsoka series will probably be best watched next, though that isn't out yet.

You can kind of do Rebels and Mandalorian S2 in either order, Rebels comes first release-wise and chronologically but you're hopping around the timeline anyway, and I think Mando S2 serves as a pretty solid re-entry for the character the two series' share. I watched them in this order, and it piqued my interest as to what that character had been up to between here and Clone Wars, which Rebels answers.