First and foremost, you have to take such a course (one on one). Once you graduate from such a course, you can think about issues clearly. Next, avoid concepts that are underspecified: breathing (instead of fricatives); speaking freely; tongue stress; point of resonance; etc. Just master things listed in some standard course: for instance, Accurate English A Complete Course in Pronunciation Rebecca M. Dauer 246p_0130072532 for AmE.
Then, there is another naive assumption foreigners entertain: acquiring an accent is same as putting articulators in a certain configuration, so that they can speak like a native. This assumption has led many self-learners to acquire all bad habits: I see such folks in many conference calls at my work. Articulatory configuration is helpful for those who want to do voice impressions (VI), since these VI folks are not L2 speakers. Piotr on youtube has a series of lessons on how to change the configuration of vocal tract, etc.
More knowledge, the better. Knowledge is the cure. That's the case in singing as well: 90 percent is the knowledge; 10 percent is the execution.
- For Teachers