Dear Sekar,
You should find where your problem started from. Ofcourse, you had identified that you are having complex.
Please note no one is perfect speaking english in india. so, don't worry about it.
First of all, you start speak with available words in english for conversation and over a period of time and you will definitely find improvement in your style of english and usage of words. Read some english news paper which are very ordinarliy understood by every one (simple english). I used initially indian express then change to The Hindu slowly once I felt understood. Never mind to converse with anyone, only thing is how the people understand your communication. Do not underestimate your speaking skills.
Also make others to speak english with you than your own language, otherwise Your learning from them won't be possible. This is how to learn from the opposite person which you interact.
Do not get into thinking about what you had spoken while speaking (like whether I used propositions correctly, degrees correctly, sentence conveyed are correct or not etc.) what ever you had spoken are out and will not come back unless opposite person react to it. He will take care of it.
I am sure your kind of people are perfect translator because during the thought process, you always feel to form sentence of speech in your own language and then try to convert to english before delivery.
Please try to see that what ever you feel should be english and through the words/sentence as it is. Later on you will find art of language skill improving.
You can even see few people use some fillers during conversation that " you know, emm, yes", in order to keep the continuty of the speech ON.
Hence don't worry about what you don't know. keep speaking what you know....
Ironically, I have been improving my english style last 10 years for MNC companies, but I end up with Japanese MNC where in I used to speak with telegraphial speaking to them, which is absolutely comfortable for my Japanese superiors.
with kind regards,
RAGHU