I am also trying to polish Kadda.

These are I discovered

and following in these days. Maybe it will help you.
Watch English movies with English subtitle not Sinhala subtitle

. And try to understand that.
And listen their pronounciation carefully. Try to follow them.
Think in English everytime. As a example, I will wash my car today, I have to do excercise today.. like that
Exchange sms with your friends in English.
Try to talk in English. Do not worry about mistakes. Mistakes make man.
If you don't know how to pronounce any word, use this site
http://dictionary.cambridge.org/
You can find any word pronounciation from UK or USA.