If your interview is taking place soon, you should focus on having more than one answer for every possible question your interviewer might ask you. As well, try to provide the same answer but with different wording. Practicing these on your own will help you speak more fluently during the interview. However, if you are looking for some permanent improvement, then more frequent use of English is definitely the best way.

Practice! Surround yourself in it. If speaking is your main problem maybe you should try watching some English/American movies with subtitles and practice speaking along with them. That really helped me remember Chinese characters when I was younger. And I also feel like it'd help you pronounce the words more precisely.