One thing that has helped in addition to voice shadowing is reciting a poem written by 北原白秋 (きたはら・はくしゅ). It’s called 五十音(ごじゅうおん). This is a poem people who speak for a living use to focus on their enunciation. I find speaking in Japanese similiar to saying tongue twisters. For that reason, I say this poem every day in addition to other speaking exercises to improve the fluidity of my speech. This practice gets one used to the variety of sound patterns often used in Japanese. Here’s a link with the poem on YouTube 発声・滑舌トレーニング ～北原白秋「五十音」 - YouTube