I sometimes hesitate using answer or comment. In this case I didn't hesitate because I didn't think giving a link was worth an answer. (I suppose my subconscious was reluctant to see me gain undue upvotes for just giving a link I always keep handy and that it costs me no effort to research.)
After @Anonymous's comment (as a reply to my own comment) should I post my original comment as an answer? Well others have answered but I can see the point in some cases in preferring practical advice on how to improve one's performance rather than a linguistic explanation - however good it is.
And wouldn't writing it as an answer make it more available to others who were looking for help in pronunciation?
Or maybe should there be a wiki where to list tips and links that are not specific to one question? After all the link to the animated library of the phonetic sounds of American English is useful to all questions on American English pronunciation.