Andressa, in my experience as a student of German and Spanish and later a community tutor here on italki, the best solution is to speak. It seems simple but it's true. It takes time but the more you speak, the more your brain makes faster connections and activates more of that passive vocabulary (i.e. the words that you understand when you hear but never use yourself). AND when you speak, don't be afraid to make mistakes. The more mistakes the better because over time your brain will adjust and they will become less and less.

Hope that helps.

Jason