I can read write and understand english but when I try to speak the words do not come nicely and lot of mistakes are done.Afterthat I undestand what mistake I did.

Something that may help is listening to music in English and watching television shows in English. This is a technique one of my friends used when trying to learn the language. He said it was very helpful.

Practice makes perfect. You need to keep on talking. You are realizing your mistakes by hearing them, so I would say keep on talking. It will get better.