I realized there are two types of issues: 1. Some sounds in English don't exist in other languages and you have to learn them "from scratch". For example the "flap T" in butter. Or the particular American "r" (constrast it to the Spanish rolled r for instance). 2. Certain sounds I DID know how to make, but didn't know WHEN to make them because spelling is so unreliable. For example, a word like "color" has two "o" letters but neither of them makes an "ou" sound - in fact they make two distinct sounds. For these, I realized you just have to practice it until your mouth "remembers" how to pronounce the word differently (i.e. creates muscle memory).
Youglish is great for fine-tuning specific words.
I also recommend BoldVoice (disclaimer: I'm a cofounder). We were YC S21 and built the app to help non-native English speakers improve their pronunciation with videos from Hollywood speech coaches and instant feedback via speech recognition ML.