Accent coaches are great. I worked with one in the context of learning an Irish accent for theater in college. You learn IPA as a tool for discussing sentences

Accent coaches are great. I worked with one in the context of learning an Irish accent for theater in college. You learn IPA as a tool for discussing sentences and get someone whose mouth you can watch closely without freaking them out and who will watch and understand your mouth position well and provide immediate feedback. For some language transitions though you have to start out retraining your brain to hear sound distinctions before you can hope to produce them. The L-R distinction in English, for example, is particularly hard for Japanese speakers because they can't hear that there are two sounds. It can also be very helpful to enlist a native speaker with the target accent who is a coworker. Basically give them permission to tell you after every conversation what you said that wasn't in the target accent.