I think first of all try to think in English because you know it very well that when you was a child you learned Hindi but how? you know them by your observation power
you was not know about Hindi also but by observing,practicing you was able to speak Hindi now very fluently
use the same case here just try to think in English and just speak it even you was wrong also
first try with simple words
and the day will come you can speak English fluently
just try it I think it might helped you
the more you spend time in reading (book, novel, newspaper) the better your vocabulary is going to be. Always keep in mind that you are looking for new words. ☺
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