For the phonetically uninitiated they are almost a waste of time. For those who want or have to learn to pronounce English a few articulatory descriptions may be of help every now and then - less helpful with English vowels than with most consonants. But other things are important as well, if not more important. You must be able to hear the difference(s) between the sounds, rhythms, (non-lexical) tones, gradations, etc. of English and your respective mother tongue; and you must be able not only to discriminate these phonetic features when used by native speakers of English but also when YOU speak English.
Here are two suggestions:
- Fraternise with a native speaker of the opposite sex - or the same sex to be seemingly politically correct!
- Monitor English natives speaking your mother language (= L1) with a moderate to strong English accent. As soon as they can no longer attack you verbally or physically, try to imitate their way of speaking your L1 with an English accent! It's revealing! And when you manage to do this, use this very same accent when YOU speak English.