I am k***** [name removed]. My native language is not English so I have a problem in the pronunciation of word "r". I want to know that where we should pronounce it and where not and what are rules
[Obviously s/he means not the word r but the letter r.]
Where should the EFL student pronounce the sound r? What advice should one give? It all depends.
• For a simple life, and if your model is American English, pronounce r wherever the letter r is written.
• However, if your model is RP or a similar form of BrE, or Australian or New Zealand English, or to fit in with those around you in Africa (for example), then you should pronounce an r-sound only if the sound that follows is a vowel sound. So there should be an r-sound in red, arrive, very, tree, address, purity, but not in hard, firm, north, persuade, standard, modern. At the end of a word — as in better, far, near — you should not pronounce r if the word is on its own or at the end of a sentence; but you may pronounce one if the word is followed, without a break, by another word beginning with a vowel sound.
More importantly, what is your purpose in learning English? If you just want to understand and be understood, then pronounce all the rs. If you want to fit in with native speakers in some particular place, then you must learn to do as they do. If you want to pass school examinations for which the examiners require that some particular type of pronunciation be used, then you must fit in with their requirements.
It is important to learn not just where to pronounce r but also how to pronounce it. If, as your name suggests, your language is Arabic, which uses a tapped r-sound (ɾ), it is worthwhile trying to acquire an English-style approximant r (ɹ).
I am afraid an answer along these lines would disappoint K****, who would doubtless prefer a clear short answer. And anyhow his/her command of English would probably not be high enough to understand fully what I say.
Probably a better answer would have been
Go and ask your teacher. Or ask your friends.