Who has advice for my problem

Hi, Can you give me some advices? I can write and read english well, but it is weird that I can not say it well. Whenever I want to express an opinion or myself, I feel my brain turns to blank and don't know what should I say.

Is that because I seldom to speak to others? How can I speak english more often in a place where there is few foreigners?

Advices are highly appreciated!

Cheers

Achell