How can I improve my English? Which is the best textbook for the same?

Refer to the dictionary and daily learn new 5 words and make sentences from it. Talk in front of the mirror. Assemble your friends and parents and speak in front of them as this will help you in building confidence.

Dear, You need to read newspaper and English articles on daily basis. Try to communicate with your close friends or close one and ask for feedback. Even, you can take classes from British council to improve the English communication. All the best.