Find a pronunciation guide for your target language, ideally in your native language. That allows you to focus on the sounds that are different from what you already know.

Go through all of the sounds your target language has. For any sound that is unfamiliar, create a flashcard.

There are two kinds of flashcards you can make:

It also helps to add anatomical pictures of the correct mouth and tongue position to produce the sound.

Example French:

Pronunciation guide https://lingvist.com/course/learn-french-online/resources/french-pronunciation/

Example flashcards