The first baby step in learning a language should be learning the letters of the alphabet and then correct grammar. Then comes phonetics, which I bet most schools in Nepal rarely teach their pupils. I was lucky to have a dedicated English teacher who held free weekend sessions to cover this aspect of the language. Perhaps, like most schools, my school also did not approve a lesson plan to cover this clearly neglected aspect of a spoken language.
Before that phonetics thing came along, I had this personal experience of the downside of not realizing a correct pronunciation. I used to be an active spelling-bee participant. The pronouncer, who happened to be department head at a local college and held a terminal degree from the UK, asked the participants to spell a word which sounded like "beree". Even after providing us with the meaning of the word from Oxford Advanced Learners' Dictionary, none of us could spell it correctly. In the end, the word turned out to be the little old frequently used word "bury" which we all used to pronouce as 'booree" or " buhree" or something like that.
In the foreign country like UK/USA/Australia, I think one needs to emulate the native speaker when it comes to pronunciation for a few reasons that comes to my mind now. Firstly, if you try that communication can go smoothly between the two counterparties. Secondly, if you pronounce a word correctly, you will less likely to be ridiculed and the counterparty will most likely oblige to what you are trying to get out of him/her. Accent and pronunciation I believe are two entirely different beasts to be tamed. Pronunciation can cover individual words but accent and tones are things you can learn over-time through constant practice with / exposure to / observation of native speakers.
If you are not sure of a word/idiom/expression/phrase/proverb, do not use it for wrong usage or pronunciation might even go as far as  triggering the Third World War.
For example,
Upon being asked during a nice welcome dinner about how the food tasted, an impressed immigrant guest exclaimed "Oh! simply AWFUL". Frown gathered upon every listener's face in the room. Then she realized she had confused one of the words with "AWESOME" but it was too late.