I found that frequently recording my voice and playing it back immediately afterward helps immensely. Up through the start of my junior year of highschool I did a very poor job with pronunciation in general and what I thought I sounded like, sounded nothing like what I did in fact sound like. I got a portable voice recorder midway through my junior year. I like poetry, so a few times a week I would spend a while (maybe a half hour) in the evenings reading poetry into the recorder and playing it back a stanza at a time. If I didn't like the way it sounded, I would repeat the stanza (or the particular line in that stanza that sounded wrong) until it started sounding right. Within a few months I very much liked the way my voice sounded, and instead of having people telling me I talked funny, I occasionally had people complimenting my enunciation. (As I side effect I also became able to read out loud which was something else I used to have a lot of trouble doing)