Dear Venkat,
Everything begins from the origin. Our origin is our family. Start talking to every family member only in English. As our friends said, whatever it is, think in English and try to express what you want to say in English.
Your grammar could be corrected day by day. For this, you would require a good friend or relative who is good at grammar, vocabulary, and is always, if not most of your time with you.
It is not true everybody uses all the words they say in a day. Perhaps you can list out the sentences you are required to use frequently. For example, start like this -
1. At home - Getting out of bed - "Good morning, where is the toothpaste and my toothbrush, is the coffee ready? Is my dress ready? Where is my lunch pack?", etc. Leaving home - "Goodbye, darling, I will be back in the evening by 8 P.M. What do you want me to bring from the market? Do you want a cinema ticket? Is there any medicine to be purchased?", etc.
2. Reaching the office - "Hello everybody, good morning, how was yesterday? My friend... so and so... why did you not call me up for yesterday's dinner at... Today I will treat at..."
"Where is the file I left/kept here yesterday?"
Pick up such small, simple sentences that do not involve complicated or advanced grammar to start with. After familiarizing yourself with such small things, then you will learn how to converse with longer and more advanced English.
Your success lies in identifying what is incorrect grammatically, in pronouncing them, pass between words, etc. If you can find friends who will help you in this manner, you will become a master over time, say in a few months. Of course, there is no magic that will help you master English overnight.
As many friends said, you will learn how to pronounce if you watch TV news.
If you write down whatever you could speak one by one and give those sentences to someone who knows the language better than you, ask them to correct grammatical errors in those sentences, then you will correct them and speak better in due course.
To improve further - you have to learn some of the frequently used phrases, idioms, present, past, future tenses, how to & where to use vowels, active & passive voice, positives & negatives. That's all. Read all kinds of English materials, newspapers, magazines, books, novels, etc., to learn how English is used in modern and day-to-day affairs.
After all, it is the headache of the persons you are going to talk to, then why do you worry?
One best way should I suggest, make friends from LKG to 8th Std. select girls, (don't pick up boys they will spoil you), you will learn lots of English, its pronunciation, very quickly. After all, they are also learners like you, no matter both of you would commit errors, learning by committing errors is always good as you will never repeat such errors.
All the best.
Kumar, Bg.