What is the best way to improve my English speaking ability?

Answer 1

There are several ways. In order to determine which strategies would be best for you I would suggest that you schedule a lesson with an experienced ESL teacher who can determine which strategies are best for you.

Answer 2

To some extent this will depend on your native language and what you're talking about.

But I strongly recommend regular practice with people whose first language is English. Meet with a variety of people if possible. If you find it difficult to get English speakers to volunteer, offer to meet them over a cup of coffee or tea. If you make a mistake, say, in pronunciation, they will catch it and help you get it right.