Pronunciation
Pebbles in your mouth? We do not advise you to practise, like Demosthenes, with stones in your mouth. Your goal should be to make yourself understood. There is no need to try to sound like an Oxford professor. Many excellent speakers of English are proud of their origin and the way they sound. Pronunciation and hearing Many learners have a common problem. They can not pronounce some of the English speech sounds, and what's a bigger problem, they can not hear the difference between some of those sounds.
Sometimes there is another problem. You may be hard of hearing. You may want to have your hearing checked.