https://www.engvid.com/english-resource/50-tongue-twisters-improve-pronunciation/ Try these!

Peter has the right idea, but just to elaborate a little further... There is a technique called "Shadowing" that I think works very well. Just find some recorded material and repeat it over and over again with the recording, with the goal to eventually speak at the same time as the recording. Just try very hard to perfectly emulate the speaker and your pronunciation will gradually improve.

Watch movies and pretend you're the characters and repeat what they say.